Hard to say for sure but my guess is they were looking for a handout. The are the most incredible animals I've ever seen. One of my earliest encounters with them was during a tournament in Melborne, Florida about 13 years ago. I was on a spot I'd prefished the day before for trout and saw two dolphin in the area. Back to the same spot on tournament day and I see them again. I'm not catching squat when one of the two surfaced not 5 feet from my kayak with a trout in its mouth. The dolphin rises halfway out of the water, tosses that trout straight up three feet in the air, catches it on the way down, throws it back up, catches it, then does it one more time. The last time the dolphin was almost completely out of the water using its tail to stand up above me. That trout was flapping just like a tuna each time it was thrown and that dolphin caught it between its teeth as sure handed as Willie Mays. I was in awe. I always believed it was showing me how much better an angler it was than I as it was making that chuckling sound the whole time.
Years later I came across a pod of 5 dolphin that would often be in the same area of Flamingo Everglades I fished. Every time I would see them I would give the same knock on the hull of my kayak to let them know I was on the water. I studied there every move across a flat as they knew the deeper channels that cut across the shallows and found the areas they often stopped to fish corresponded with the better areas I had caught fish. It got to where I could usually predict exactly where they were headed and I would often take a short cut in less than a foot of water that they couldn't navigate, to beat them to the place. My short cut was about half a mile shorter than their route.
One day as I saw them headed for one of my favorite spots on the opposite side of the bay, I took off to beat them there. The biggest and lead dolphin in the group peeled away from the others and came straight at me from well over a 100 yards away. I could see a big hump of water coming at me and I knew it knew what I was up to. I quit paddling, turned my kayak directly at it and hurriedly got my camera ready. That dolphin looked like a torpedo, it swam the entire distance completely under water at an incredible speed, in less than 4 feet of water. It was one of the few times I'd wished I had a GoPro camera. I was in shock when it flew out of the water directly in front of me and made the perfect cannon ball splash that completely soaked me. The delayed shutter of camera completely missed the dolphin in the air and only getting the first part of the splash when it hit and the hump of water as it returned to its family. I just sat there laughing and thinking what a truly incredible animal they are.
I sometimes tell folks this is why I rarely fish topwaters any more.
A good rule of angling philosphy is not to interfere with another fisherman's ways of being happy, unless you want to be hated.
Zane Grey, Tales of Fishes, 1919https://vimeo.com/73372194