The user who posted it is a pretty prominent leaker, who also goes by the name of King Zell. He accurately named a bunch of games that would be announced in a Nintendo Direct, including the Link's Awakening remake and Mario Maker 2. (though I'm not sure if he specifically said that it would be a Link's Awakening remake, or a 2D Zelda game in general - still looking up sources on those)
He previously said that he'd heard about something that was described as being like "if Mario was on Playstation", and recently made a post claiming that he "just dropped by to say halo to everyone." More information can be found
here.
People are thinking that he's hinting at the Master Chief Collection coming to Switch, which he followed up on with further posts. I'm not sure how reliable he is (given its popularity on the Wii U, a Mario Maker 2 on the Switch seems like a no-brainer), but that's why people are speculating about it. The presence of Microsoft-funded (and previously exclusive to Microsoft consoles) games like Ori and the Blind Forest, and Cuphead, make it seem like a real possibility.
It doesn't necessarily mean Master Chief in Smash is going to happen (as many have pointed out, if getting a game on the Switch meant that a character was definitely going to be in Smash, then characters like Tracer, Ori, and the Troll from Troll and I would all be in Smash Bros.), but people like to speculate.