It sounds to me like the man made a good shot, but didn't give the bear time to die. The other hunters said that they saw the bear sitting and laying down then getting up an fleeing. I'd say if they backed off and let the bullet continue to do it's work, this never would have happened. If I had to guess, I'd say that they were so excited about the size of the bear the immediately tore off after it. Unless I see it drop, I don't even do this with deer!
WylieKy