Looked like the mag tried to drop, he popped it and racked the slide.
Might’ve hit the mag release by accident during the draw or handling. Either way, it’s a training issue.
CC
I didn't see the mag drop. Hitting the mag and racking the slide is part of the "tap/rack" drill. May have just been a failure to eject.
It could also be that he squeezed the trigger before it went all the way to the reset point and he just thought he had a problem, then instinctively did the tap/rack drill. Glocks have a nice short reset but I guess it's still possible.