Keep in mind that the Bajo-Kazooie tweet from Phil Spencer was likely a calculated move. If they don't get in, everyone will blame Nintendo. If they do get in, everyone will praise Microsoft, Nintendo will do all the work, and Microsoft gets money from Nintendo for an IP that they haven't done anything with for years.
As for the leak, I think the revelation that the supposed leaker no longer works at Marina might be pretty telling. Someone could very well have looked up the name of an advertising company that works with BN to make the fake seem more credible, then just looked around for the name of someone who could feasibly have been responsible for the leak and chosen the guy's name, not knowing that the guy had left and not bothered to update his profile. Definitely seems like a believable slip up.