These were probably Peter Island moorings, and not Sea-Secure ones; although I've personally got on 2 empty boats that broke their moorings and brought them back in the BVI, once in The Bight on Norman where the mooring broke away as yours did and once in the North Sound where a cleat line hadn't been properly secured.
In the BVI especially one needs to check moorings, usually only the pendant and the first couple of feet of main mooring since most of the damage is caused by charter
boats running over lines. Sea Secure does an adequate job these days of diving
on their moorings.
I believe that last season the Moorings stated that someone should always be aboard when on a mooring after they (almost) lost
a boat that drifted off at the Baths; I'm not sure if they still have that requirement.