I have about a 6 inch Regal tang and he does the same thing. He picks up pieces of rock, crabs, anything he can swims to the top of the tank (30 inch high) and drops them - seems to be a great sport for him
Just the other evening I watched this tang knock some snails off the side walls of the tank.
I have a "baby" regal tang also which is just about 3 inches and he does the same thing.
I think it's a trait of these fish to assert themselves??
Rick