I'm not sure its any form of racism so much as curiosity. I definitely ask everyone (of every race accent etc)where they are from or where they grew up during the introduction phase and if they say New York then fine---I don't normally probe but if they say they were adopted from Korea but don't remember it then that's cool too. Some people jump the gun and start with their original place of birth or families origin when I'm just trying to figure out for example if they are familiar with snow and the like ie did you go to school in the south. While it does sound like some of the people your son encounters are jerks the questions about origin aren't really wrong in and of themselves. I suppose some of this is in my case about making the transition to work/school easier for new people because we get a lot of international people but its also fun to learn about different cultures. So here is the problem if your son assumes these questions are negative then they will be. I think that if he randomly picks countries people are going to assume he has more issues than he already has and if he gets into the habit of lying about a specific country it might come up at something important like a doctors appointment or job interview. I would ask him if when he looks at the pages of national geographic he is at all curious about where the photos are taken...this might yield further insight.