Actually I do know the story or most of it now. I also know one of the people involved and i know more about them than I should have too since I have dealt with their behavior before.
I am not saying that I support the OP unconditionally and I have heard things about them doing the same. However a person should not have to make a post like that in the first place, if you fuck up take responsibility. I have in the past as well. Not for stealing others works but for being misinformed. I say sorry publicly and take the original post down. That is what being an adult is.
As I stated I have dealt with one of the two before. Hiding behind a diagnosis of anxiety or depression or life being fucked up and not dealing with a situation is not an adult thing. Mob mentality or not I am for calling out wrong when I see it. If someone post something about the OP doing it I would call them out too. I however am not in that fandom so I doubt I would see it.
Calling out someone for stealing ones work puts blame on the person stealing, I have given a few warnings about my own stuff being stolen. You know what kills fandoms? Not the calling out but the fact people DO NOT CALL IT OUT. As one if not the most prolific writer for the ikesen fandom I have earned the right to call someone out if I see them saying my work is theirs. If my readers message me and say you know this is like your stuff and I see it is something I wrote then I have every right to say something. Now I have years of experience dealing with people claiming my work so I handle it differently then most because my skin is thicker but to someone just starting it would not be as forgiving. It could completely devastate them to see someone with a large following say it was theirs. Then The he said she said game happens.
I tend to mind my own business unless I know one or both of the creators for the reason I don’t like drama. However when I have people assuming that I am completely ignorant on people I have to speak up. I have seen many fandoms rise and fall because people are too afraid to speak up. If the idea that someone can take your work regardless of the context of your own behavior then kiss all your fandoms goodbye. I for one will say something. That is what being an adult really is.