The snorkeling equipment didnt materialize out of thin air so of course he had it with him, and if he had it with him she would have known about it since she was living in the same room as him. Hard to hide that.
As for the currents, she is gone is she not? Obviously such currents exist.
There is a massive current called the Carribean current just offshore, that goes in one direction, allways. If you get caught in that you are going with it in a big hurry. It doesnt matter what the surface conditions are, it can be as smooth as a lake. Currents run beneath the surface, that is why they are so dangerous, you don't know that they are there unless you are a local. A current will NOT bring a body ashore, you need wind and wave action for that to happen and by all accounts there wasn't any of that.
I don't need to be a local to know, just by looking at the shape of the island, the nature of the southern coast line and the direction of the deep water current, that that particular part of the island would be very dangerous to go swimming outside of the protected water of coves.