Invasive Polyps Vanished

It has been a little over a week since I bought my Yellow Tang and Frog Spawn Coral. During that time I also picked up a rock with button polyps. Since I made these additions my supposedly invasive Clove Polyps have completely disappeared. See my previous post on the polyps. I noticed that at one point the polyps were no longer expanding and only the stalks were visible. Now, there are none to be seen anywhere in the tank whereas previously they were on about 4 or 5 pieces of rock. I had my water tested today and there were no nitrates, nitrites or phosphates present in the sample. So, they didn't die off because of degrading water conditions. I made no changes to the lighting either. So what caused them to die off? Is it possible that the Yellow Tang ate the Clove Polyps? Did the other corals in the tank out-compete the Clove Polyps for nutrients? Even though the Tang picked at the rocks a lot I never saw it eat these polyps. Also, since the stalks were visible for a while it seems unlikely they were eaten. Perhaps they only like the conditions of an immature tank. I may never know. I'm just happy they didn't take over the tank.