The realization that one's stereotypes are wrong (or at least have many exceptions) is a beautiful thing, if sometimes confusing and even painful for some. Now you know first-hand how misleading stereotypes can be - any stereotypes, not just regarding Americans. It's not to say that these generalizations have no value, but we should strive to judge individuals by their own merits and flaws, not by what we think "their sort of person" is like. It's a life lesson that far too many people never receive.
My big grasp of that - and it was a notion I'd realized before, but this is what really drove it home - came when I spent my junior year of college in Japan. There were students going to my school from a LOT of different countries: Japan, of course, but also Sweden, Poland, Russian, Myanmar, Sri Lanka, Thailand, Taiwan, China, France, Indonesia, Congo, Mexico, Latvia, the Netherlands, Finland and others I've forgotten. Going to class with them, talking and laughing with them, getting frustrated and cussing the teachers, the kanji and the entire language with them, it opened my eyes to the fact that people are people, no matter where they're from. There are good people, bad people, most people are in between. Sure, we're different in a lot of not-insignificant ways, but we're alike in a lot of significant ones too.