I am european too, but USA flag just represents west for me way more than the flag of European Union. It probably depends on a person. I personally can't imagine myself carrying American flag either, but when I see one I instantly think of the 'West' unlike the EU stars.

>Why? No one considers an American flag as a symbol of Western world since about 2000.

People do, I do, american flag is the most 'Western flag' I personally can think of.

>Most Czechs don't really have any need to have flag of their own country, why would anyone own an American flag?

Dunno. They probably bought them specifically for the demonstration. You can buy american flag for 6 dollars in some army shop on your way to the protest easily.

Nah they are probably czech. This is sort of 'counter-demonstration' against the recent anti-nato, anti-EU, anti-west, pro-russian protests. They probably have the american flag as a symbol of the western world.