I do agree with your general point, though: I would expect your average European to have a better understanding of the politics of the US than your average American would have of even a prominent European country like Germany.
But a random European can easily say that the parent is sooo stereotypical of the USA :-).
Note that I believe there is some level of European identity. But "European condescension" is not really part of it, I would say. What the OP may have felt was maybe some "non-US condescension"? I think it could be a thing. The OP said "believe me I know Europe better than you, because I live in Europe AND I am an American" (which somehow implies that being an American made them more knowledgeable? Not sure). The answer was something like "dude, it's so American to believe and proudly say that you must know better because you are American", I felt. Sure, it's condescending. But I don't think that whatever the European shared identity is contains a "they are condescending against anyone non-European".
I believe that there is a bit of an asymmetry between US people and... well the rest of the world, in that the WHOLE world has some level of insights into the US. Whether they want it or not, for many different reasons.
However, the US don't typically have a good insights into... the rest of the world. Which does make sense: the rest of the world is pretty big.
Of course the US is more complicated than "they elected Trump". Sure, there are 50 states. But everybody knows that (be it just because your president repeatedly threatens to annex Canada as the 51st state ;-) ). People in the rest of the world do not need to "live in the US" to have that level of insights, because the US makes sure they do, by force if necessary.
The mere fact that you don't seem to be aware of this asymmetry at all suggests that you over-estimate your "pretty good insight into all of Europe".