As explained
here, some streamers / influencers have privileged access to Blizzard, whether it's pure friendship or business accointances. They get teased so they can tease. It's free hype, without revealing anything you get these "talking heads" nurturing their viewers / communities on a "what's next" basis.
In this case, it's not your average joe, both Towellie and Preach are quite connected regarding WoW / Blizzard, whether you hate or like them. Are they just blindly trolling, talking garbage for more views? Are they fed bullshit by their "sources"? Any of that could be true, especially when there's definitely
some agitation about encrypted Alpha clients.
But the "it's not at BlizzCon therefore it's not true" argument is idiotic, Blizzard announced Legion during 2016 Gamescom and with both major videogame conventions getting cancelled amidst coronavirus and alpha F&F invites at the horizon (with datamining frenzy), they're not gonna wait months to announce anything. What's on the table right now might be more than what was on the table during 2019 Blizzcon. Stuff changes, especially when about one of three people on Earth are confined right now.