I didn’t say this because I didn’t want to dump on my own fellow countrymen quite so comprehensively, but yes.
I’m happy to dump on my fellow countrymen. We can be really ignorant.
Based on my knowledge of people from China, India, Pakistan and Finland, most people seem to have a very filtered knowledge of their own countries’ history.
Including how much of what they “know” is so either one-sided or fabricated as to be worse than nothing.
Those last two statements are accurate even given that the OP knows the person’s parents are from India. The fifth I think is also accurate even given that, because the OP in the original post said they were going by the appearance (turban) and name, and there’s not to me a whole lot of difference between going by the name alone and going by the knowledge that the parents are Indian given that there’s no indication the OP has any idea how the colleague was raised and given that the OP said specifically they didn’t know where the co-worker was born and gave no indication of knowing whether the co-worker has ever been in India even briefly, let alone lived there, let alone lived in the area in question.
The first three (posts 4, 23, and 25) were posted before the OP gave the information that they know the parents are from India, which was in post 26.
I will give you 4 (post 29) and 6 (post 74), with the caveat that those posters might have missed post 26, and the further caveat that most of the sixth is accurate even given that the co-worker’s heritage is known to be Indian.
Yeah. The person in question may well have been born in the USA, and is a “westerner”.
Plus which, that style of business suit is also worn in India (not, of course, to the exclusion of a lot of other types of clothing.)

The average American is dimly aware of American history.
And much of what we’re dimly aware of is often wrong.
I suspect that we’re not the only place in the world with this problem, though.

I suspect that we’re not the only place in the world with this problem, though.
Maybe not, but I bet we are the most proud of it. 'Murica!
Was he Sikh?

We can be really ignorant.
The average American has below average intelligence.
I was aware of a notable number of Peruvians of Japanese descent - because of this guy Alberto Fujimori - Wikipedia - but not of a similar situation in Brazil.

The average American has below average intelligence.
“Think of how stupid the average American is, and realize that half of them are stupider than that.” - George Carlin
Only under the new-but-unimproved (in fact quite the opposite) mega expansion of what defines “racist”[1] c-would this be considered such a thing.
It’s one thing if it turns out that the poster is wrong and the colleague’s ethnicity is not in fact Indian - and we cannot know but may reasonably assess he is ethnically Indian (but male Sikhs do wear turbans).
There’s as much danger in pretending to disregard ethnicity and/or culture. Let’s say OP were one of those dolts who pretend to or actually navigate life based on “I don’t see color [ethnicity, culture, etc.]”, which to the vast majority of PoC is offensive in some way.[2]
Had OP not said a thing, the result may still have been a poor reaction for different reasons. Goal posts can change in a hot minute. How young is the person? What are his parents like? What’s his personality? Do OP and he get along, hardly know each other or …? Many questions arise.
Reasonable conclusion is that this person is often harassed inside and/or outside work and so is on a hair trigger. I’d approach privately and attempt to clear the air.
[1] … pretty much any damn thing someone deems to be racist, includingvbut not limited to mere acknowledgment of a person’s being, whether or not - (and all too often these days not) in fact racist but perhaps something else/less egregious, if anything, and/or the manifestation of a (routinely benign v. malignant) bias or prejudice born of ignorance or other factors.
And everyone - no exceptions - holds biases and prejudices, both positive and negative, benign and/or malignant.
[2] To be sure, there are many also contrarian AF humans who will flip the script to suit an agenda or preference depending on who it is that is doing or not doing a-b-c, and don’t let slip an opportunity to do damage. If you’re a person they like, no problem; if you’re disliked, problem. Simple. Humans are as a general rule hypocritical, emotion-driven and so easily offended/disturbed creatures.

Was he Sikh?-
And if so, is he better now?
But seriously, the OP should look at this as an opportunity to be the bigger man. Take him to lunch as a way to apologize and explain that you’ve learned something here. Maybe get to know him a little better, possibly pick up a good Chana Masala recipe (kinda sorta kidding).

There’s as much danger in pretending to disregard ethnicity and/or culture.
But who’s asking for this? This in itself is another assumption with a lot of racial baggage.
PoCs generally are realistic that people will gather certain hints from their appearance, especially if it differs from ‘the norm’ in the US.
The main issue for this thread in particular is that ethnicity was the primary or perhaps only lens through which the person was seen. Not even culture - the co-worker was culturally American.
The solution to this is not the opposite, i.e. to ignore ethnicity entirely. It is to view a person’s ethnicity as simply a part of the whole. Just as we would our Mr Peter Hartmann, the accentless German immigrant, who somehow nobody treats any differently from ‘normal’ Americans despite his cultural and ethnic differences from that norm. We don’t think it strange to treat such a person as a normal, culturally American individual. But it is not yet normal to do so for people with other ethnic backgrounds, whether or not their families have been in the country for generations.

But who’s asking for this?
I didn’t mean for anyone to infer people are asking for this, but there are many members of the Pale ‘Woke’ Tribe who insist that behaving as though they’re color blind is a best practice, whereas most (not all) PoC would, if asked, say “If you don’t see my color, you don’t really see me.”

The main issue for this thread in particular is that ethnicity was the primary or perhaps only lens through which the person was seen. Not even culture - the co-worker was culturally American.
Neither of these conclusions can be drawn from the OP’s post, unless you’re referring to follow-ups (if so, I didn’t see them - I came in based on a SD digest email btw).

Wasn’t just you
He said he knew it, but based on what seemed to be potentially unfounded assumptions by the OP, I wanted to verify that he actually knew, vs assumed. He still hasn’t said how he knows what seems like a somewhat personal bit of information about the coworker, but he confirmed that he “knows” it, so I let it go.
I think people are leaving out bits of the OP-stated “facts” because some of them could be mistaken assumptions or erroneous conclusions. They are conclusions that we don’t know the basis for, so some people are going on only the more solid basic facts.
It is in no way being disingenuous to not be willing to take unsupported conclusions at face value. If the OP tells us that he knows this because he’s met the parents and they told him they are from India, fine. If the OP says he knows they are Indian because they have “Indian” names and dress a certain way, and look and speak a certain way, then it’s not “known.”
So, yeah, what you said was singling out a colleague based on his appearance. And this offended him. But he didn’t say, “you are an evil person”. He said, “what your said was racist”. That’s an opportunity for you to improve, and not a dismissal of you. He’s probably aware that you didn’t have any malicious intent. But you hurt him, and he’s doing the honor of telling you so you can improve.
You can take the constructive criticism, apologize, and avoid doing it next time. You might even thank him for letting you know. (If you are friendly with him.)
We all make mistakes and hurt other people from time to time. A good person learns from doing that and is more careful next time.

It’s one thing if it turns out that the poster is wrong and the colleague’s ethnicity is not in fact Indian - and we cannot know but may reasonably assess he is ethnically Indian (but male Sikhs do wear turbans).
Even if he was right about ethnicity, it was still racist. We can explain it to you, but we can’t understand it for you.

Neither of these conclusions can be drawn from the OP’s post
I’m pretty much drawing the first conclusion from this in the OP itself:

And I replied “Well, you our kind of our resident Indian expert in the company” (as he is the only person with Indian heritage in the company).
So, if we allow for extreme credulity, maybe that’s not explicitly stating that ethnicity was the only consideration, but it’s heavily implied and even used as justification for the action.
For the second conclusion, it’s later in the thread, but the OP was unsure if the co-worker was born in India or not, implying there was little else than appearance and name to draw that conclusion and with a reasonable presumption (ok fine, I’ll grant this is not definitive) that the co-worker has at least spent many of his formative years in the US.
And, for what that’s worth, that’s another one of those annoying questions - “No, what’s your birth/real name?”

Those last two statements are accurate even given that the OP knows the person’s parents are from India.
I’m not entirely sure he does, given that he thinks wearing a turban is a sign of being Indian. Are we SURE his name in Indian?
There’s nothing wrong with not knowing that. People are not obliged to know everything there is to know about other countries. However, it means one is best off assuming they don’t know, and not ascribing knowledge or ignorance to others based on the color of their skin and what garb they might choose to wear.

I didn’t mean for anyone to infer people are asking for this, but there are many members of the Pale ‘Woke’ Tribe who insist that behaving as though they’re color blind is a best practice, whereas most (not all) PoC would, if asked, say “If you don’t see my color, you don’t really see me.”
I call bullspit on this. What you just typed is at least a strawman. No one is suggesting that noticing his color or turban or parents is the problem. It is making assumptions based on that. And I don’t think you can make a claim as to what “most” PoC think. The most you can do, assuming you are a PoC, is to say what you think. Which is the point of the whole OP.
And if caring about minimizing another person based on uncontrolled externals makes me “woke” then I wear the title with pride.
Yeah, most of the people I see taking the “I don’t see color” line are not liberal. They’re coupling that with “racism doesn’t exist anymore.”