Nudibranch ate my colt coral shocker!

Just scooped this thing out of my tank! The strange thing is i have been practically watching him consume my Colt coral for the past 2-3mths!! I moved the rock which the colt was on about 3mths ago, when it was 6-7" tall; hoping it would move and instead I thought id damaged one of its arms [it appeared to go white and look dead like, which in actual fact was this guy! Now the colt is only about 4" tall and i was about to assume I was to blame . The nudi or slug or whatever it is only became apparent when he moved, which since then hasnt been at all apart from today! Ill post some more shots - the nudi seems to have camouflage just like the polyps on a colt..