Is the European Union not a thing anymore? Does being a part of that not make you European? What does European mean if not for people who live in Europe?
To be fair America has 50 different states and a lot of them have totally different cultures. Texas compared to new york for example. Would that not make your statement equally as dumb?
The European Union is a union and not a country, the EU is pretty irrelevant here since there are lots of Europeans that don't live in a member country. There are lots of cultural differences and languages.
Of course everyone in Europe is European but generalising Europeans that really doesn't have that much in common (except living in Europe) is most often pretty stupid. Europe is very diverse in culture, climate, economy, politics, etc.