I don't think those are all from people trying to hit a target downrange, necessarily, I'll bet some are from people not following rule #3.
Probably others are from novice, inexperienced, over-zeaous, etc, shooters that try to shoot far "too much gun" for them, first shot recoils the handgun way up, they pull the trigger again during the process (not consciously or intentionally) and it fires again, hitting the ceiling (the same way at least one woman has died when giving a far too powerful handgun by some incredibly stupid guy who thought it would be funny)