Unfortunately, a certain individual broke Twitter so the full thread cannot be viewed without being signed in; but I think this does help add some perspective to the original tweet.
That link's not working for me, but from what I could find the drama is about this image, right?
I'm not going to claim to be an expert in generated images, but I don't see any particular signs pointing toward it being faked. It's a bit "dreamy" looking, but that's not exclusive to generated images by any means.
Also, I'm inclined to believe their denial here. I don't see any particular reason for wotc to so strongly pledge to not use these methods and then immediately use it for advertising. And even it being somehow unintentional seems like a stretch. The inner (and outer) communication at wotc has never been great, but this would be excessive even for them.
Who cares if that technology makes a way shittier version of what he made? Think of all the shareholder profits once we've automated everything good out of the game!