Yeah that's what I thought, but having spoken to him, it seems it was just a fluke. He thinks that maybe his "MT" clan members helped him reach the 9999 feat (by only shooting at others etc.) so I don't know how "real" his ranking is.
I'm also trying to get at least 1 star on every Grand Prix, but it's really difficult, blue shell there, red shell there. Of course it's been said before, but it's damn annoying.
Not entirely sure what the rank is based on, but I think it's predominatly time. Therefore if you fall off a circuit, it will naturally effect your time and rank.