Incredible, right? It's the Boston Marathon, he sets off two bombs, seconds apart, and he does it with a cell phone, which is the best guess right now for how the actual attacker did it! Well, yes, that is incredible in the original sense of the word: not easy to believe. Why would setting off bombs from a bar let him win the marathon?
It wouldn't, which ought to have been the first clue that this isn't a real clip. It's two unrelated clips. Here's the real one that references the Boston Marathon:
So, once again, the internet gets in a tizzy over nothing. Let's hope the retraction goes just as viral, so that Seth Macfarlane can continue making offensive comedy in peace.