When zombies with armor drown, they will drop all of the armor with 100% drop rate and in perfect condition
This bug allows users to obtain armor in perfect condition if they drown a zombie with armor, with a guaranteed drop of everything, including held items
In the video, when I open my inventory, you can see that the armor has no durability lost, whereas when you normally kill a zombie with armor, it may drop and the durability is very low. If you attempt to reproduce this, none of the armor won't drop (Though there is a chance they may pick it back up again. If that happens, you can kill them and it will still drop all the armor/tools, but the armor might lose a few durability points because you damaged the zombie.)