Interesting, when my urchin ate clove polyps it was only the polyps that weren’t receiving light after I had moved a rock above the coralThis seems to be a contradiction to me.
Over the decades I've seen a few times damaged coral polyps and tissue eaten while apparently healthy polyps and tissue next to what's eaten is left alone. When animals that don't eat coral suddenly decide to eat some I'm now inclined to just watch to see happens. If they are removing damaged or unhealthy tissue that might give rise to Brown Jelly or something else they've done me a favor in my book.