If it was some kind of international forum with a delegate of Americans, granted, that would be pretty annoying.
The subtext here is that Republicans have obviously tried to claim that criticism of them is criticism of your country and therefore distasteful. Some liberals, progressives, have responded by taking the bait and basically, saying "Yeah, we do suck. The world should hate us. Etc."
While you in the rest of the world may think that statement is exactly correct, for some reason it has not led to electoral success.
Obama has been clever enough to side step the whole thing. He has been withering in his criticism of the current administration. At the same time, he has made a theme of not running to be president of only the "blue" parts of this country. And he has backed this up with speeches about issues that, while not changing his more or less standard Democratic positions, express respect for people who disagree with him.
So, the spontaneous "U.S.A" chants were directed at both the current administration and its supporters, and whatever parts of the opposition that have given up on this country. It was a way of saying that we can get past partisanship and actually start thinking about doing what we need to do to fix our real problems as a country.
And, I did see your smiley. But I thought an explanation of what this means to someone living in the U.S.A. (speaking only for myself, of course) might be useful.