The details are hazy, and it certainly could be wrong, but it's not completely unfounded. Mearls took it on himself to investigate the allegations against Zak S* and asked for people to send him statements about their experiences with him. This is not something you should ever do unless you have been trained to do it.
On the specific allegation of doxxing by Mearls, if you search for it in the trash fire formerly known as Twitter, you find links that point to other links that point to other links and never lead to anyone with firsthand knowledge. However, a regular poster on this forum who knows the victim heard the story from her and
summarized it thusly:
"The email in question [describing alleged abusive behavior by Zak S] was sent from an email address which she created specifically for the purpose of sending it to Mike Mearls. She did not use that email for anything else or tell anyone else about it, and shortly thereafter she received harassing emails from Zak at that address."
That's still secondhand information, of course, and assuming it's true, it still leaves open a wide variety of possibilities, from carelessness to hacking to deliberate malice. And it does not preclude the possibility that people inside WotC with an axe to grind seized on the whole business as an opportunity to push Mearls out; Mearls was removed from control of D&D and has now been unceremoniously laid off, which certainly seems like sufficient punishment. Nevertheless, this claim has a little more behind it than just the social media echo chamber.
