Assuming the video is real, it was almost certainly faulty ammo.
Even if that isn't the case, ammo that fires outside a gun isn't nearly as dangerous as the same bullet being fired from a gun. This is because, instead of most of the energy going to accelerate the bullet, the energy is simply split between the bullet and the casing. The casing has far less mass (in most cases) than the bullet and so a round that fires outside of a gun would see the casing fly off and a higher speed and in the opposite direction of the bullet.
More importantly, when you fire a round from a gun, the very high pressure that builds up inside firing chamber and the barrel of the gun is what accelerates the bullet toward whatever the gun it pointed at. If there is no gun then the expanding gas simply dissipates immediately after the bullet leaves the shell casing, robbing the bullet of nearly all of the power that it would have had, had it been fired from a gun. Depending on the round, Black Cat fireworks would likely go off with more intensity.
That, of course, doesn't mean that someone couldn't get injured by such a misfired round but it isn't as "scary" as the guy in the video seems to think. It could put out an eye or whatever but it isn't going to be anywhere close to having been shot with the same round through a gun.