Was the DM in the water, or was he making a statement based on the belief that it should have been the right wreck? It might be an honest mistake that they themselves did not realize, or they might have realized they made a mistake and decided you would not know the difference.
A couple of years ago I was starting a Belize (Ambergris Caye) vacation and got a warning from someone who was concluding theirs. They had booked a trip with our operator to the Elbow on Turneffe Atoll. This is a big trip for which you pay extra, and you have to start very early in the morning. When they got to the dock, there was a problem--no DM. After a long delay, the operator located a DM, but not the one they had expected. They later learned that the night before had been some holiday, and the DMs had been celebrating into the wee hours. The scheduled DM was not to be found, and the one they found had been present throughout the celebration.
The boat headed out, and the DM lay on a bench half or fully asleep most of the way. The trip did not take anywhere near as long as they expected, and they got suspicious. The diver had a map, and he could clearly see that they were not at the Elbow. He challenged the DM on the spot, and they got into an argument. At one point the DM said they were at the "Little Elbow."
They did three shortened dives and got back to dock an hour earlier than expected, despite getting such a late start.
They raised Heck in the office and were eventually given their money back, but if the diver with the map had not been on his toes, they would have accepted the trip as it was presented to them. The boat crew clearly did not think the customers would know the difference.