He has no idea how hard it is to hit a moving target, and probably less of an idea of how to hit a stationary one with a firearm.
People who haven't tried have no idea how difficult it is to hit a stationary target with a short-barrelled handgun, even when your nerves are calm and steady.
I used to be in a pistol league shooting the National Match Course, using a target pistol with extremely light trigger pull, no detectable trigger creep, and a long barrel. Even so, it was amazing how very slight misalignment or improper grip could cause terrible misses.
With your heart thumping, adrenalin flowing, in fear of your life, with a man running to kill you, I think it's remarkable to get as many good hits as he did.
And in that situation you'd have to be a fool to stop firing before the attacker hits the deck.