I'm French and I did not know salted popcorn even existed until I went to the UK (other than salted butter caramel popcorn). I just asked for popcorn and always got sugared popcorn...
In the UK at least, at a cinema you'll choose between sweet or salt popcorn, you can get salt/sweet/mixed popcorn in supermarkets, and Butterkist toffee popcorn is a common thing
Sure, but sweet and butter/salt are equally available (literally, pretty much every brand does both) so to generalise that Europeans think sweet when thinking of popcorn is ridiculous.
Corollary: 50% of beers in the US are watery piss, so when Americans think of beer they think of watery piss.
If you ask they will do you a mix in the cinema too!
In Belgium people will look at you funny if you ask for salt on your popcorn