Why not teach the basics of cave diving before introducing a more complex and advanced method of diving. I'm willing to bet you a steak dinner that he didn't have some back problem, or a shoulder mobility issue, or whatever the reason dujour is for diving SM
Doing things without a reason is never smart in my book. And most of the reasons for wanting to dive SM in OW are bs, as far as I'm concerned. Its analogous to rebreather for a new diver, to me. Learn to cave dive, then lets learn the specialized stuff. Hell, we were all debating if intro divers should be allowed to dive doubles, and yet here we are giving the tools to brand spakin new (potential) cave divers a tool to get not only far, but in small, unforgiving cave.