We were there and while we didn't see the shark, we talked with the crew of the canoe excursion that leaves from the lagoon. They were the ones who reported the baby shark. It was a tiny hammer head baby that wouldn't hurt a human, would only cause a bruise if it tried to bite. The reason the lagoon was closed was because of concern of the Mama hammer head probably nearby waiting for her baby to come out of the lagoon. Mama couldn't have gotten into the lagoon due to her size.
There is no netting or barrier preventing fish or other animals entering the lagoon, but the depth isn't deep enough for a large shark.
We did see some awesome octopuses in the lagoon beyond the blue and white rope by the rocks.