This is the evidence most people point to when making that claim, which is, admittedly, not exactly a smoking gun. The truth seems to be less "Mearls forwarded people's complaints to Zak" and more "Mearls inadvertently name-dropped two critics to a man who is notorious for launching harassment campaigns against his critics" at least as far as the evidence lies, which is definitely not the same thing, but... it's still pretty terrible. Just less intentionally so, I guess.
In case it hadn't been clear, I'm honestly largely ambivalent on this crap at this point. Fred Hicks was doing almost exactly the same awful crap at around basically the same time-frame (though at least Fred apologized for it later), back when OSR was the Big Hot Thing and bigger designers were desperate to pander to that audience in any way possible. Again, a direct apology or some indication a lesson was learned by all this would be really, really nice, but it appears to be asking for too much from WotC or Mearls at this point and it's pretty obvious the pressure for it just doesn't exist anymore.
Enabling a serial harasser and abuser is pretty awful mistake that ends up getting a lot more people hurt, and that deserves an apology, but at the end of the day, it's still just a
mistake. You learn from it and do better in the future.
I just... I just hope they actually learned from it.
Edit: By the by, I apologize for my own part in perpetuating a rumor that didn't seem to have much leg to stand on. I've taken the liberty to edit the wording in my previous post to more accurately describe the bad thing Mearls did in this instance.