I’m not even totally sure its a mutation and there doesn’t seem to be a lot of consensus on what it is or what causes it. It happens in cultivation and the wild, I believe its common to see chanterelles with this type of growth. I’ve tried to look it up and the reason that is stated most often is that it’s due to pollutants, specifically petroleum contamination. I’ve never had anyone give any evidence for this, though. I do recall reading https://www.sciencedirect.com/science/article/abs/pii/S0953756208606723?via=ihub, it states that rosecomb is the result of endogenous genetic instability but didn’t want to pay to read the whole thing.