Tough guy. Scary.
But a few other thoughts cross my mind. Like:
I'm not sure it was not screaming that saved him. Only a fool would think that the bear didn't know he was still alive. Clearly the bear didn't consider him food or worthy of killing. The bear simply got bored or felt it had had proved the point. Had the bear wanted him dead he would be.

It is possible the bear thought he was a territorial rival or was too close to her cubs. There is the possibility the bear was young and just looking for a playmate. Between bears such behavior and holding the head down and gnawing is both how they play and how they work out dominance when fairly young. That sort of behavior doesn't do much harm if your another bear. Humans are much more delicate. Played with that way we tend to break and die.