You make a good point. There is a lot of history in Asia, and plenty of animosity stemming from centuries of intercultural conflicts that sets Asian peoples apart.
As to American hubris, a lot of that may be cultural indoctrination, as Americans are provided a very American-centric curriculum in primary school, at least. I don't necessarily think that's solely an American trait, as I expect anyone discussing the group of which they are part will use that same kind of expression.
Edit: rereading your comment I now see you meant that Americans assumed the person they were conversing with was an American. Sorry for my misunderstanding.
hi valued-customer, yes lot's of history and different cultures, and the geographical locations , even food, make people look different in long period of time.