I had forgotten about this thread until it resurfaced recently. So, I guess an update is in order.
I had occasion to be in the neighborhood of the dive shop in question back in December and decided to stop in to check it out. The "shop" wasn't easy to find. It turned out to be in the owner's garage, out back of his house. The owner is a likable guy and we talked about various aspects of diving. We eventually got around to talking about vintage dive gear and I learned that he actually thinks diving old equipment is fine as long as the gear is kept in good shape and the diver knows what he's doing. So, I related what had happened out on the lake.
After he calmed down and his language was once more fit for human ears, he told me that the instructor in question has never worked for his shop. Rather, he had simply used the shop as a contact point for recruiting students. The shop owner is not, himself, a certified instructor and relies on freelancers to train anyone who comes in looking for a class. The guy in question had done more harm than good for the shop's business and, I was told, was banned from the shop not long after my encounter with him on Grayson Lake.
The owner was concerned when I told him I'd posted my experience on SB, until I assured him I hadn't named his shop. His operation is marginal at best and he doesn't need any adverse publicity, so I promised to keep him, and his business, to myself.
Before I left, he handed me coupons for ten free air fills for when I'm diving in his area and apologized for what happened.