It's the bodies whose bodies have changed. Because their bodies have rotted or other reasons, and the light in the ancient tomb is not very good, the skin of such bodies looks like zongzi, and they usually wear funerary objects on it, so they are called zongzi.

It is easy for people to feel fear in that closed and narrow place. Plus they already know that this is an ancient tomb, and they already know that there will be danger in their hearts. If there is an emergency, such as a corpse or a zombie, that person's spirit will collapse, so they are called zombie zongzi when they meet a zombie, so they can get some psychological comfort and not collapse.