Board Thread:False Info and Speculative Discussion/@comment-4705573-20160408003331/@comment-26879545-20160412121754

^ Stiles had the 'real' body. The Nogitsune's body was, essentially, a real-time replica of Stiles' body. They were still connected, somehow, but they resided in two different bodies after the Nogitsune split them apart. So, when Scott bit the Nogitsune's arm, he wasn't biting Stiles, he was biting the Fox's "physical form," so to speak.

I agree with you, though. Logically, Stiles would have been in the duplicate body and should have been turned from the bite that expelled the Nogitsune. The thing is, we just have to chalk it up to the writing. It was a convenient asspull that allowed them to keep Stiles the human while also mind f***ing everyone that tries to explain why, by all intents and purposes, Stiles should not even be human at this stage in the show.