Dear Jesus. I have straight up killed one back to bare skeleton and had it regenerate. My name says zoa fanatic but candy canes are my passion. I can tell you 100% it’s not tissue damage. A damaged head would not heal and grow bsck around the effected area like that. The tears turn a brown color similar to brown jelly disease ans basically rot away leaving a small portion of tissue. They can regenerate from literally no tissue showing. If that was tissue damage with that much tissue remaining on the head then it would have at the very least begun regenerating by now.
If you LOOK at the skeleton beneath the heads you’ll note it’s not the same color. Newly cleared skeleton has a stark white color to it that this does not. Further, it’s called “trumpet coral” for a reason. The heads grow in the shape of a trumpet. That is not trumpet shaped. It’s some parasitic intruder