While I'm not sure I buy into PapaGenos' theory about Banjo only being secured at E3, largely because it depends on a lot of assumptions, I 100% agree that this is not a fake leak that has been created by some guy trying too fool us, it's such a convoluted situation with so many layers to it, I think that's completely out of the question, I really do think that the printing company had these materials sent by Nintendo.
In the scenario that this isn't our roster I even find it more likely that Nintendo are protecting the real roster by sending out fake banners for the first iterations of promotional prints, so in case something like this happens they've got themselves covered, and if it doesn't they'll feel more comfortable sending the real deal for actual merchandise and such. Now I would find that incredibly disrespectful to any companies they send those to, and there's the question of whether Nintendo would even be allowed to do that with the 3rd party characters, but crazy things happen in the industry these days, and I just can't convince myself that there's some guy out there who's using his one of a kind intelligence to mess with Smash fans. Seriously, if someone in a crime movie had set up such a convoluted plan I'd have called it unrealistic.
Again, that does not mean that it isn't fake, the video game industry and the measures companies take to try and avoid leaks these days are sometimes crazy, and I could see Nintendo being particularly cautious in this regard as the previous Smash was the subject of one of the most notable video game leaks ever. But I'm confident that this isn't just one guy pulling everyone's nose, because the story has gotten way out of hand for that to be the case.