At least they are silly questions and not offensive questions.
For some people it might be part of an assimilation process, but it is likely to be for a variety of reasons.
Some people are curious, some might be trying to get to understand him a little better, some might think he's weird and are trying to affirm that in their own minds and some people might just be being rude.
He could ask them why they want to know and take it from there. What he sees as silly questions might not seem so silly to others.