I have seen this happen many times.. Schooling fish(pilchards) chased to shore by predators.. Jack Crevalle("Jacks") in that/my case... Most would flop around until they got into the water again.. but not all.. Amazing sight..
I have seen the same thing on the Texas coast but never that many. Most common for me is to find mullet or rain minnows packed together in a very shallow tidal pool right by the beach where they went to escape a predator and then got caught by a falling tide. I have just scooped them up with my cap.