Many, many years ago I almost drowned while snorkeling in Belize. Out with friends (locals who could swim like a fish) I tryed to keep up.
I could not! Before I knew it, they were out of sight and the boat was far away. I waved but the girls on the boat did not see me. Swimming against the current, no vest or BC, a fair amount of salt water inside me, I did make it (only half dead)-------------Learned a few things:
1. Always leave a boat operator onboard, keeping a CONSTANT count---NOT every 30 minutes as in the news report.
2. Always anchor down current and have the snorkelers swim up current. If they get in trouble the current will bring them back to the boat.
3. Have your own BC or rent one (and check it out)
4. Have a experienced person with the group who is also responsible for diver count.
All this should go without saying but from the news report it looks like the tour guide did non of the above.