Not gunsmithing-the lights slide right on the rail and are tightened down. Simple operation
But always best to do when unloaded and with your booger hook off the bang button.
A lot is made of Glocks lack of a “Safety” IT has a variety of mechanical devices that prevent discharge unless the trigger is being pulled intentionally. Much like a revolver
The primary safety is between the shooters ears. He didn’t use it
I guess he decided to rest the muzzle on his foot while he attached it.