Are you talking about people who have anuses/rectums that are so stretched out that when the person opens up his hole, it flares out like a blossoming red-hot rose or a peony? If so, I think that is a result of fisting.
I don't think that mere anal sex does stretches the anal sphincter muscles as much as a fist does, from what I understand.
And does it heal? I am not sure. It would seem that the anal orifice would be permanently stretched to a degree, and maybe even be somewhat like ruffles on a woman's or girl's outfit.
But I am not an expert on this sort of thing, although I have looked at photos of escorts's holes on RM and wondered, "Hmm...I wonder if this person gets into fisting."