63 year old killed by mama grizzly in Yellowstone

In this case, I wonder if somehow the hiker got inbetween the cub and the mom while on the trail.

Could be. Could also just stumble into one when it decides your presence is a threat. Some Yellowstone bears have been around man and aren't very skittish. Just like people, there are some that will just be ornery and will be aggressive. The problem with an encounter with an adult 600 lb. grizzly is that it is powerful, thinks it's the king of the forest, and has enough claw to tear you up quickly. A knife and bear spray may thwart an attack but the fighting would probably be over before you could get either in your hand.