Looks ok to me.. recent split that is healing (you can tell by the tiny new tentacles starting to grow at the rim/mouth area). It will take about a month to fully heal but it still looks healthy to me so just give it time.
I never really thought about it much before, but you mentioning this, especially about mushrooms, brought back some memories from my first days of reefing. I used to have green hairy mushrooms that would spit its guts out after a water change. I am wondering now if it had to do with water quality issues (lack of understanding at that point by me) because I was using RO water from grocery store dispensers at that time.I looked at my Anemone at night with a flash light and found it deflated with his guts out. They were definitely his gust and not poop. It stayed like that for a while. In the morning it looked fine again. That was weired. I saw a mushroom ones do that for maybe 15 min. What does it mean? Do they just air the guts ones in a while? I did a 4Gal out of 30 water change yesterday. Could that trigger it? There is so much I am learning about the aquarium critters life cycle and behavior that I have not discovered on the net yet. ]