The frags are on rather heavy plugs and were both on their side with the tips pulled far into the gap under the rock, which was a good 3 inches from their original position. I'm not sure how a Filefish would do that. If the Filefish had chose to eat just those two frags then I doubt he would have tried to hide them after and the flow wouldn't put them in that position.
You have any crabs in there? Crabs will move **** all over in my tank if not glued down. I have watched emerald crabs chomp off tips and base of frags. Pistol shrimp will also drag anything they can towards their den for more protection. If you have either I would suspect it's one of them.