It breaks standards, plain and simple. If the diver were to get injured or worse, now the DMT, in this case the OP, would be on the hook for the injury/death. The DMT should not be showing any skills to an OW student, full stop.Why would it be dangerous when the instructor is right there and just lets the DM or DMT show a couple of skills, as long as the DM/DMT is showing them correctly? It's not that the DM or DMT is conducting the training.
Showing the skills is conducting the training btw.