"Wow, what a weird story. I've never heard of a bear acting like that."
Not that weird, really. It was simply a bear in predatory mode. Fortunately, there were enough people around to rescue the prey.
This is behavior is not common, but does happen somewhere in North America every year or so. It's more common in Canada, for some reason, than in the States. Again, not usual behavior, but certainly in the broad spectrum of normal behavior – thus the advice to fight if a black bear attacks.
FWIW, if you read the reports, it's surprising how often the predatory bear is killed (if the bear is killed) by the victim or helper using a knife – much more frequently than with a gun! (Haven't read of one being killed with a knife on the end of a stick, though!)