I have wondered about this myself - I see it with stripers, hybrids and black bass. I believe they can hear the other fish popping on top and that triggers them. Maybe they hear it or sense it through the lateral line. But it seems to happen a lot, fairly quiet, then they are blowing up everywhere, then it quiets down again for a minute or two.
When used to have an aquarium, I'd tap lightly on the cover before feeding them, soon as I'd tap, they'd be swarming on top ready for that food.