Of course, that's right. An earlier draft of my comment had the phrase "to whatever extent they're representative" in it.

However, I think crude inferences can be made from comparisons between the students from different cultures. We're all highly selected in that environment, but there are definitely differences that jump out and it seems reasonable to attribute those to the home cultures.

Something that helps with that for me is knowing people from different class backgrounds in India and China, specifically, so I can partially adjust for that variable.