That honestly sounds as plausible to me as saying the majority of Europeans thinkg 2+2=5.
Forgive me if I have a hard time believing you. Because I can definitely tell you Americans understand where their government spending comes from, and I have a hard time believing that Europeans are somehow less educated on this.
For most Europeans, a tax is an unclear bill at the end of the month, leaving them feeling powerless to do anything about it.
One thing I learned from living in America is that people here are much more engaged in civic life and politics. The UK (which I also lived in) is perhaps the exception to this European rule.
I'm American but have spent a lot of time in Europe -- France, Spain, and Germany mostly. I have seen nothing to indicate that Europeans are ignorant of where government spending comes from. They seem just as smart as anyone else.
And national elections in Europe also seem like large news events, even if the campaign season is (thankfully) a whole lot shorter.