When you unload a revolver you're looking at it from behind, and if you just dump the casings into your hand you might not notice. Maybe that happened.
Or maybe they only replaced one bullet with a blank.
Technically Brandon Lee was killed by a bullet. They removed the powder but left the bullet (for appearance sake since it was a revolver and would be noticeable). Since there was no powder the bullet didn't fire out of the gun when the trigger was pulled but the primer (which wasn't removed) igniting created enough force to put the bullet in the barrel where it got jammed.
No one noticed the jammed bullet, and when they next fired it with blanks this time (powder charge, no bullets) the powder was now forceful enough to fire the bullet out of the gun.
Essentially they accidentally made a revolver into a breach loaded firearm.
Says it was a homemade blank made from gunpowder and glue. Depends on the construction but the glue "bullet" (probably just a plug to keep the gunpowder in) should explode in the barrel and shoot out basically dust.
However you can't guarantee the glue plug would fully disintegrate and at close range the debris can be moving fast enough to cause damage and can be hot enough to burn.
I have an acquaintance who, if anyone ever talks about the subject of sex Ed around, he will insist that they will just teach the kids about blood play and it will spread STDs.
So that's the level of logic we may be dealing with here.
Without the cam how is YouTube supposed to know you are drinking your verification can?