While the media (though they don't seem to intend to) definitely paints a far different picture, as others have pointed out, the small handful of people who incited the riot were there with that sole purpose. The outcome of Game 7 really didn't matter to them, they simply went to cause trouble (and, of those arrested, most were also involved in previous issues such as the 2010 Olympics and '94 Stanley Cup finals fiascoes). Sadly, it stirred up a mob mentality, and the situation simply escalated.
That said, it still does reflect poorly on the city and our country, and is a bit embarrassing. It's honestly more of an embarrassment to be associated (by being Canadian) with the people who did nothing, though. Those who went to start the pandemonium...well, there's assholes everywhere.