It seems credible to me. There's a chance it's fake, but the idea that OpenAI agents might exploit a wiki that accepts edits via GET doesn't seem unrealistic given what happened with the Hugging Face incident.

The edit are there on these wikis (and others not mentioned on the post, but for example on wiki4d, the dlang wiki).

It's very difficult to argue for any fabrication meant to harm OpenAI when the traces are all over the internet if you look for them.