From the Remington ballistics table:
9mm Parabellum muzzle energy is approx 350 ftlbs x 11 rounds = 3850 ftlbs.
40 S&W muzzle energy is approx 450 ftlbs x 11 rounds = 4950 ftlbs
45 Auto muzzle energy is approx 450 ftlbs x 11 rounds = 4950 ftlbs
3" 12 ga rifled slug muzzle energy = 3000 ftlbs.
Assuming the bears never had experience with hunters or firearms discharge they probably thought all humans were cute and tasty just like the two greens thay just ate. Once the warden began firing his handgun at point blank range, the bear probably didn't associate the noise and shock with the nearby humans.
As shown above, the accumulated energy delivered by 11 rounds of even 9mm at point blank range is pretty significant. Of course having colleagues nearby armed with shotguns probably gave the warden a measure of reassurance as well.