Board Thread:False Info and Speculative Discussion/@comment-26601629-20150817180018/@comment-13895380-20150817184852

Oh, also, they already know that Parrish is supernatural (presumably the only supernatural at the scene), but they don't know what he is, so it would make sense to be suspicious of him. Stiles also probably knows that Parrish survived being in a flaming car in season 4; in the two times Parrish stole the body while Stiles was there, the environment was very hot and had fire or smoke.