How reef safe are porcupine puffers supposed to be?

Hey guys, I've had a porcupine puffer for quite some time now. My water quality has been improving and I decided to buy 3 frags. 2 zoanthinds and a small kenya tree frag.

I placed them on a rock and half an hour after, the kenya tree was on the sand bed. It seemed fine so I thought that maybe a current knocked it down from the rock. However, I went out with a friend and when I came back it was upside down in the sand and there was nothing there but the glue that was used to attach it.

Did the Porcupine puffer fish eat it? I was under the understanding that puffers basically were only not safe when it came to inverts like snails and shrimp. Or maybe something else happened? could it have disintegrated from falling in the sand in a couple of hours?

The only other fish I have in there are chromis, a foxface and silver batfish.

 

all puffers are not reef safe IMO, this includes tobies.... to my knowledge though they have a preference for stony corals not softies..