Random attacks or seemingly unprovoked attacks can happen anywhere, anytime.
I agree if this had happened on a commercial airline flight in Canada or USA it would be big news here. However there have been afew incidents in recent years where passengers have gone ballistic, and at times have lost their lives being subdued.
On the other hand, I watched a news interview, of the passenger on the fatal Greyhound bus you mentioned, who was sitting directly behind the victim. He stated the victim had fallen asleep with his walkman blaring, and the accused snapped.
Case in point, here is a video I suggest you DO NOT watch if violence is too offense for you to watch, however it was played on the network news. This happened after the Greyhound tradgedy, in Philadelphia on the subway. A father and his young son are standing, asleep taking up two seats is a young man, with his walkman blaring. The father sits his son down, very calmly, and goes into a violent attack against the sleeping young man.
Click here for Video
I lived in Los Angeles in 1988 the year freeway shootings and attacks took-off!, there were 100 shootings in a 90 day period, one third of the attackers were caught, and most of them had no criminal record - just snapped. It lead to the movie
Falling Down.