Because it's pedantry. I checked 4 dictionaries for america or american. Or just type "america" on whatever search engine First thing for 3/4 dictionaries was the US or its citizens. If anyone ever means to refer to the continent they usually say north/south America or "the Americas".

Go to any country other than the US and ask a local "Are you american?". They're all gonna say the same thing. "No, I'm Mexican/Canadian/Chilean/etc."

Whenever a word has multiple meanings, you're supposed to use context to figure out which one is being used. Well, the article title mentions the US government. It's also a very common phrase with a well established meaning. Check out Green day's american idiot, for example.

Really doesn't take a genius to understand what op meant.