Absolutely true. No way they guy could have overcome a mob attack by 300 people. Also, if you’re going to get shot, it’s better to get shot by someone not aiming. Sure you could die, but it’s less likely for a vital organ to be hit if the shooter is just pulling the trigger in panic mode.
I suspect the perp just walked up to the people laying on the ground and shot them in the head or shot the ones who were scrambling for the (apparently locked) doors in the back.
If a half dozen people had charged him, he could not have taken aim at any of them. He would certainly have hit a couple before they swarmed him, but in the end he would have been tackled and disarmed.
It’s like a bayonet charge. The enemy is caught off guard by charging troops. They shoot wildly when the target is moving rapidly towards them and even more wildly when there are several targets moving in. At that point they are as scared and panicked as the people they are shooting at.
But war tactics are not taught in public schools where even the mention of a gunman can get you expelled.