Perhaps they're deliberately being a little pedantic?? Instead of asking them 'why', tell them exactly how you feel. If they understand you, there shouldn't be a problem. Maybe try addressing the fact you have other things to talk about besides your nationality, in a straight forward manner as opposed to beating around the bush, so they know exactly how you feel??

If you think they're genuinely upset/hurt because you shared your honest opinion regarding their approach to your autism, maybe send them an article about "neurotypical" people to represent how you're feeling in a humorous way - that you haven't only got Asperger's or your nationality to talk about. Maybe they'll laugh and see it from your point of view?? I'm not sure, I haven't experienced this...

At least you're handling this with integrity and respect - some people on the spectrum wouldn't understand nor know how to approach this type of situation.