What the writer meant was that corn is a treat. Sunflower also. Fed by itself, chickens love it. Cut out the treat and they will eat their whole foods.No, it's not.
Corn is the base of the vast majority of chicken feeds out there - it's no more "candy" than sunflower seeds, millet, or any other grain. Feeding chickens nothing but corn is a bad idea, but that's true of pretty much anything.