I have thought about it, twice even, as you insisted. Yes, it is hard to imagine any kid taking on a belligerent man brandishing a gun while facing him. However, alcohol intake by some or all parties not only alters behavior but recollection of the event, too. It could be he said his piece with his piece and had started to leave -- note the prepositional phrase "after his threat" -- when a couple of "heroes" jumped him, and his first shot caused the others to scatter. It's more difficult to picture him appearing to be unarmed, getting tackled head on and managing to pull his concealed weapon while on his back.