I disagree. I see a man who, at first, thinks he is in trouble and upon realizing that they'd like him to play? His face lights up. I don't think this is a joke, good or bad, but a brief moment of camaraderie shared between people who's only shared language is that of music.
It is worth noting that nobody is mocking the man, or his accordion, save for HERE. The passengers, clapping and singing along, the musician positively beaming...this (to me) is a good thing.