From what I know (not an expert), a 150 lb. blackie is basically a yearling that got the boot from mom. That's a time where they are vulnerable to starvation, which would explain the clearly predatory behaviour. This behaviour is rare but not unknown. In this situation, with a blackie, you fight back with everything you've got.

It may not be fair to say so, but I get the impression that this fellow may have unwitting presented the body language of prey. (Armchair assessment, I know.)

BTW, fighting even a small black bear would be no joke. One of my Great Danes is 150 lbs.; a big marshmallow, but plenty intimidating; you have no idea how bloody strong those jaws are 'til you try to remove porcupine quills with pliers ...