When I was the sole feeder of our koi they would come to the surface when they felt the vibration of my footsteps on the bridge. When anyone else would walk on the bridge to look at the fish they couldn't be bothered to come up to the surface. Now that the family feeds them, they come up to the surface whenever they feel someone on the bridge even if it is one of the grandchildren.
Many years ago, we purchased a Koi Kichi Koi Buffet; the pagoda looking wooden feeder with a string and trap door. The roof lifts up to fill with food and when the fish pull the string a few pellets of food fall into the water. After we filled and hung it over the pond it took them 10 minutes to figure it out. Now we can tell when they are hungry because we can hear the clicking noise of the trap door.
Anyone that says fish, especially koi, aren't smart doesn't know fish!