Please read Edd Speaks...he only had to risk his life to save 4 divers who were not trained for the dives they were undertaking. http://www.nsscds.org/files/uws/v40n2/uws40vol2web.pdf
You appear to have lost all sense of perspective. We're talking a diver doing a shallow dive in a benign quarry. Not exactly dangerous and the OP has no idea if the guy is trained, experienced or any assessment of skill level. Nothing to suggest (i) there'd be an incident or (ii) if there was anything would happen as you'll find the dive area itself is covered as its got a stated policy that was violated. Scaremongering on what is a common, benign situation.
You're also assuming somehow makes divers perfectly safe at whatever they choose to do.
The OP could do with someone following him around on all his dives for a while criticising everything from his kit config to decision making to buoyancy control just to see how he likes people interfering with his leisure.