I don't think this is the place to go into details about who did and said what, especially since some of the people involved are notorious for stalking, harassing, and threatening people who participate in conversations about their misdeeds.
Last I heard Mearls had been in unofficial exile to another part of the company for several months but they announced a couple weeks ago (possibly accidentally) that he'd be coming back to work on D&D stuff again, and that's when the hashtag got going.
But there's been a LOT of stuff going on and what I know about these situations is what's filtered through my feeds despite muting every variation of D&D/Wizards/etc that I can think of.