I took two years of Japanese and was president of our Japanese club for my senior year. I will have to agree if you don't spend time around the Asian girls, I doubt you could tell.
However I can tell the difference between a Hmong, Japanese, and Thai girl. But hell I couldn't tell if the chick was Chinese. Also as far as I'm concerned the Thai and Louse (sp? I'm sure I didn't spell that right) girls look the same. There are many Asian people in this part of Wisconsin because during Vietnam war we brought many over, and here in our city we housed a lot of them. So it's an asian melting pot. (BTW I'm not asian, I'm white, but have never had a problem with them)
If you never delt with them I think it would be increddibly tough, so I think it's a ligitimate question, and not quite sure why people are piling on so bad. Yes it almost sounds racist to ask.
I will however agree the question is way too vague. I would think he doesn't know any better.
But it would be the same in asking how to tells someone from the north, or the south, or whos a Jew (just an example). Just saying.
The simple answer is, if you have spent a decent amount of time around them you can kind of tell, but you never know.