They were crazy to get so close to a school of fish like that.
Just as easily it could have been any marine predator looking for lunch.
lol. I was snorkeling close to the coast near Kuaui (Hawain Island). I had ventured past where the rocks drop off into some deep areas. At first I thought my seeing a huge school of fish swimming frantically was a cool and rare thing to witness. I started toward the school to see if I could get in it when the thought occurred to me. "Why do large schools of fish swim so frantically? And how do schools of fish play in the food chain."
I too became a bit frantic and started moving and looking for potential predators. I was smart enough to dive rather than surface initially while I worked back toward the safety of the rocks. I never saw anything that looked dangerous. But on my way in, a Parrot Fish snuck up on me and took a nibble at my gold neck chain (jewelry). Scared the $hit out of me and I called it quits.