As Lois, Peter, and Stewie wait for the "Kids Say..." auditions, Peter's clothes change from a blue suit, to a gray suit, and then to his normal clothing.
It makes no sense for Brian to turn up to his first gig as a film director without having read the script and indeed without even asking what it is about, or anything at all about the film.
He probably thought he could get away with it in his portrayal as a clueless talking dog in an unrealistic cartoon.
He probably thought he could get away with it in his portrayal as a clueless talking dog in an unrealistic cartoon.