I don't know that I'd agree that the bears are black bears in the game. Black bears are relatively small (for bears) and the bears in the game are about as tall at the shoulders while on all fours as you. A black bear would be about half your height (on all fours). Granted, a grizzly is also going to be shorter than you, though not as much as a black bear. Considering no real bears will be as tall on all fours as those in the game, I guess you could assume they are black bears, though I still would pick a grizzly or brown bear (or even a kodiak) as they are all larger than a black bear on average.
Black bears are also generally going to run away from you unless there are cubs involved or you really make it mad. Unless you want to imagine that the bears are all starving and so will attack for that reason, but considering the amount of prey animals around, that wouldn't really make sense. Other bears are less skittish than the black bear.