What a tragedy. A trip that was supposed to be an exciting experience turns to horror.
We can't assume that the guides were unarmed. It'd be irresponsible NOT to be. I think the problem might have come from an attack that is swift and sudden. Especially in low light, a bear could be on the party in a heartbeat.
Alaskan guides in bear territory carry some heavy firepower, and lone fishermen often pack a .44 magnum, which probably is on the too-light side.