Timeline's wrong, he's with them still, at least as of E3 2014. He updated Mii's name to Mii Fighter.
My guess is that, to avoid leaks, the workload is heavily divied up. Our leaker is part of the CGI trailers team. He leaks both because he loves Smash, but also because leaking a game will probably hurt him in terms of working with games again, but since he's a CGI guy, he can find work in other industries. He sees models for Pac-man, Mii, Little Mac, Villager, Megaman, and WFT pre-E3 2013. He leaks. He decides to wait a long while as to see if he'll get in any trouble. By the time of the Smash direct, he leaks again, having seen models for Palutena, Shulk, Chorus Men, and Chrom by now, and having modeled Pokemon for the trailer, though not knowing who it'll be (remember, there's like 30+ Pokemon models in the trailer). E3 2014 comes around. He's heard there'll be DLC and that Lucas might get cut, and that Mii is now Mii Fighter. These sound more like employee gossip then actual firsthand accounts. He updates us. Then comes this. He again decides to report employee gossip, but ends up wrong, and finds out he is wrong about Chrom. However, he's still confident enough in the other two to believe they're in.
Alternatively, a teenager starts emailing Gematsu for lulz. That could be it too.
