I vote he was disassembling it, didn’t make sure it was unloaded, and when he pulled the trigger to remove the slide, sent a round through his hand. Then made up the drop story to save face.
That’s my bet too. Contact wound. Saw a guy with the same left hand done by a Sig. Dont remember if he was disassembling or chamber checking but he put his palm over the muzzle and pulled the trigger.