Maybe he needs to start the bear, then do nothing for a second or two to simulate wondering "what the hell is that noise?" Then a second or two of looking over his shoulder to try and identify what's happening. Then a second or two to overcome the "oh shyt" response. Then pull the gun.
This was exactly my experience. Had the bear wanted to get me it definitely would have. If you busy engaged in some other activity like fishing you better hope that it the bear gives you a warning huff.
I am no expert but the one "event" I had was eye opening.
