Yeah, the latter is what I meant, a sense of the other same-sex person as erotically enticing. It can be ephemeral, and even if you get a whiff of it it you often fold it into a sense of comparison and envy, but the fact remains that you smelt it as you were dealt it at the time, ya know?
I don’t know what was meant by the phrase, but I assume deep in their lizard brain a straight male like myself is quite capable of observing a rival male and recognizing “that guy has a lot more of what would appeal to women” without thinking “I want to get it on with him…”. I’m refering to the cues which trigger what appeals even in a subconscious way.
For example, a number of studies have analyzed what about women appeals to (most) men. Deep down, these have evolutionary bases - smooth skin and facial symmettry indicate good genes and good immune system, for example. A number of other body cues indicate things like adequate balances of female hormones. I assume the same applies to male appearances - that they signal “this guy is a good mate”. Certainly males need to recognize who would be a greater rival, in the game of evolution?
Not to mention layered on top of that is the whole attribute of personality, which also plays a large role in interpersonal attraction.
I don’t think that’s the same thing as being aroused by the person. Which is what I think @AHunter3 is describing: being aroused by the presence of, or the sight of, or a depiction of a person of the same sex. This can certainly happen even when one has no intention of doing anything about it; just as, say, a person in a monogamous relationship may occasionally be aroused by someone who’s not their partner, even though they may be genuinely monogamous and never have sex outside their partnership.
Throughout my life there have been an enormous number of instances in which I have caught a view of someone — e.g., standing in line at the theatre, or waiting with the rest of us for the subway to pull in, or on TV shown walking across the room — usually with their clothes on and not doing anything overtly sexually provocative, by the way — and found them sexually attractive with lotsa exclamation points bouncing around in my head. Almost never does that coincide with having an actual erection.
If by “arousal” we mean “engorgement of erectile tissues”, then, no I’m not referring or limiting it to that. But I’ve occasionally had those moments when the view of a male person kicked off that above-described reaction. Distinctively and overwhelmingly in the minority, whereas that reaction from seeing a female person are so commonplace that it’s an unusual day for me to be out and about and not have it happen at least once or twice. And no serious interest in following through with the reaction out of curiousity or whatever. But yes it can definitely happen and I’m assuming such is the case for a wide range of people of both sexes.
In the 19th and early 20th century, the percentage of left handed people was about 2.5%. Now it’s 10-15%. A startling growth? Perhaps not. In 1900, we should interpret 2.5% as “1 in 40 people are so left-handed that in spite of strong social opposition, they persist in leftyness.” The people who preferred their left hands but could be converted under pressure were counted as righties, the people who were better with their left hands but could manage with the right hands were counted as righties, the actually ambisinister were counted as righties, and even the people who late in life had disease or injury to their right hands were counted as “really righties but bravely managing to use their left hands anyway”. It’s not surprisingly that the number of “open” lefties has skyrocketed (an increase by a factor of 4 or 5 - when will it end!), and there’s no need to search for a mysterious environment poison causing this - it’s just that we’re naturally measuring two different things: “stubborn and strongly lefthanded people” in 1900, and “people who prefer to use their left hand to any extent” today.
Now that is a persuasive argument.
My son is in 7th grade. I can tell you that things have really changed since I was in 7th grade, some 40 years ago.
In my day one wouldn’t dare make it known that you weren’t totally straight. If anyone found out or even suspected otherwise, you’d be be teased and bullied terribly.
Contrast that with nowadays: My son will sometimes tell us, “my friend [name] told us he’s nonbinary.” Or “she’s gender fluid”. Totally nonchalantly.
Assuming that’s a reply to me - thanks 
It was.
Yes, this is exactly what’s going on.
There might ALSO be environmental stuff. There’s plausible evidence for it. But the really big thing is a change in social acceptance.