My mother worked as a nurse in California and sometimes complained about the difficulty she had understanding many Filipina nurses.
The same desperate need for nursing in the health care industry that prompted the OP probably leads to a relaxing of requirements for getting certified. It’s only natural.
Also, I can see a person working very hard to make themselves understood while in school so that they can pass and become a nurse, then stop trying as hard once they actually get in the profession and get a job. Especially if they can converse with colleagues in their native language.
I know most of my math skills have atrophied since my days in school, as well as my Japanese language skills, because I haven’t needed to keep them up since then.
It’s been going on since Columbus.
The English you get taught in class and examined on and the English you need for day-to-day work are very different; the amount of multiple-choice exams in the US means that a lot of people get through by memorizing things that they wouldn’t even be able to pronounce. I had a college professor who had lived in the US for more than 10 years and we needed to ask the students who shared the professor’s mother language to translate (the good news is, we did learn some basic grammar, since he used it in his pseudo-English). The university’s administrators couldn’t understand why nobody from other languages wanted to be part of that particular research team. I’ve also known people who memorized as much of the citizenship test as they could, but who would recite it in perfecto si esto es inglés yo soy la mona Chita.
It isn’t just nurses. The hospital I worked for had a free conversational English program, and kept sentencing doctors to go to it. It was about as popular as the diversity training, and IMO should have been just as optional (i.e., not optional). None of the doctors thought they needed it, but there were actually a couple of bad outcomes because the patient didn’t understand the doctor and vice versa. Now one was a cardiologist who had one medical degree from India and another medical degree from a US university, so he thought he was fine. He got a degree, in English, from an American university. And apparently he could understand his patients fine. They just couldn’t understand him. But communication has to be both ways, particularly with people who could get into medical trouble if they don’t understand.
And you win the thread!
Wouldn’t help much with the Hindi-speaking staff, though…
Or Tagalog.
Interesting how many people don’t seem to have actually read the thread - he’s not at work, he’s a resident in a “rehab” hospital.
Sure, but that could be a very desirable skill. 
Non-native RNs working in the U.S. must pass an English comprehension test to be licensed (although this likely varies by state).
For a period of a few years it was even required of Canadian nurses working in the U.S.
mmm
I speak just enough of that to get my face slapped or arrested if I try more than ask for a cup of coffee.
Happy to hear of your desire to learn Spanish.
You can never know too many languages. It is fun. For me it is a lot of work. But quite rewarding. I am fluent in three languages.
There is a lot of tourists here. And we normally meet in bars and cantinas. So, I have taken an interest in learning how to say “cheers “ in their language. After that the door is open and I pick up a few more conversational bits.
As I mentioned it is work for me to learn languages. I have to write everything down and then repetition.
Good luck. And keep us deformed.
Pulling a pun on me? Now I’m committed. 
Years ago I had the idea of a set of lessons titled “Speak Spanish Like a Texan.” For it I would set aside distractions like authentic accents and conversational speed in favor of basic comprehension, based on my observation that many people will bend over backwards to understand and be understood by emigrees making an effort to speak their language. We don’t demand that Hispanics or Indians speak English like native Chicagoans and they don’t expect that we will speak like natives of their countries. We make allowances for adults speaking second languages and don’t laugh or express our frustrations until we get home. That’s how it’s been for forever.
I have been promoting this here and elsewhere, but no one has done it. No, I’m not volunteering to do it.
Interesting that you can’t differentiate between ONE person who was mistaken, and the “many” that you claim.
It could be like Speak English like a Non-Mexican!
Well, some other posters have failed to notice, e.g., that the OP was talking about Hindi speakers rather than Spanish speakers. I don’t think Broomstick meant to imply that “many” people mistakenly thought specifically that the OP was the colleague of these people rather than their patient.
Are they actually nurses, subject to nurse licenses (or whatever)? Or are they just minimum wage shlubs told to do some takes that don’t legally require a nurse?
Licensed professionals. That’s where the registered in Registered Nurse and certified in Certified Nursing Assistant come from.
Having seen what my wife went through to get an RN degree/license, I find it hard to believe anyone who isn’t fluent in English could do that. Are you sure it’s not just an unfamiliarity with your particular accent?