This one’s pretty simple – out of the things that could stop a .50 caliber bullet (a mountain, tank, etc.) bulletproof glass isn’t one of them. Edwin Sarkissian decided he’d test just how little difference bulletproof glass would make in protecting anything behind it by using water bottles as targets. Those water bottles would’ve stood just as good of a chance behind a sheet of paper.
Will bulletproof glass stop an incoming .50 caliber round? Not unless they’re being thrown by hand.