Probably people don't usually carry and assault rifle with while they have they keys and a coffee in their hands. If he relied on an AR15 for a situation like this, it probably would've chilling in the house. and he would've been unarmed.This is the argument for Assault rifles
Pistol are the best weapon for self defense because you can have it on you at all times 24/7.
Rifles are more effective for hunters and soldiers, mass shooters , people who are actively looking for something to shoot.
Average AR owner isn't coming home from work with the rifle slung over his back.