I have observed this will happen when a Dolphin Pod first arrives, and then right before the final push to strand fish.
It makes sense. If there are people, sometimes even dogs, along the shore there will be no stranding.
Also if they are not comfortable at the end of a drive they work the fish schools at the edge, not on, the shore. It’s more common to end the push while in the shallow water. It’s safer for the Dolphins.
Above a Dolphin swam by me, just a few yards off shore. A rule (and law) is to stay back around 50 feet. Let them eat.