I think the muzzle was against his arm when he fired. A contact wound.
From the multiple videos I’ve seen, the Asshat was about 3-5 feet away when he got shot. asshat initially stopped, the kid lowered the rifle, then said asshat lunged for him, when the kid pulled the weapon back up and fired.
The dead skateboarder dude got right in the pump at about 2 feet, staggered away and collapsed.