You could decapitate someone with a shorter blade, Ben. Have you ever watched someone get decapitated before? Even with a really large knife, it still takes a bit of time to sever the head completely. I doubt it ever happens like in the movies, where someone swings at their neck just once and their head goes flying off their shoulders.
That just means he took his time with said decapitation. Most Canadian citizens are pretty timid, and I imagine that most of them went in to shock while the attack was taking place.
Sorry if that was too cryptic, but eh . . . everyone knows the world ain't all sunshine. The sad part is that this isn't the first time someone got mutilated on a Greyhound bus. I'd never step in one of those things without some type of protection.