Can we start taking wishlists from the boards and handing them to gaming news websites as inside info? Because that's what it looks like is happening.
It's not a new phenomenon or anything.
Look at how easily people bought into other wishlist leaks like Miahstorm and Tower of Smash, and compare that to how hesitant people were to accept the ESRB leak. Two text-only "leaks" with ridiculous claims gained traction after getting one or two things right (Chrom not being playable in Miahstorm's case, the presence of Game & Wario and Great Fox stages in Tower of Smash's) and were still believed even after massive blunders. One leak that had a mountain of screenshot and video evidence was immediately labeled fake and, at one point, was even considered debunked for the dumbest of reasons, like "zomg two human characters have facial structures that match up!!!1111".
It's all about what the leaks themselves implicate. You can say all the crazy ridiculous crap you want, but if your roster has characters like K. Rool and Ridley on it, you're basically guaranteed more believers.