Most sensible explanation so far. It accounts for why they would be worried about hidden, automatic cameras much more than the ones regular tourists have, where you can see when they're taking a picture or getting a good video angle. Also, most tourists don't take pictures of what's going on behind the counter, so you can catch someone trying to overtly do that, but a hidden camera would make that harder to spot, leading management to be more paranoid about built-in cameras.

On top of that, "concern about the health department" has a much higher prior probability than "mafia collusion with major fast food chain".