Meghan Trainor - Lips Are Moving Lyrics Meaning

I think lips are moving is about a couple who seem happy together. One night, the man comes home smelling like perfume. The scent is mostly on his collar. The woman knows hes been cheating on her. " I know your lieing your lips are moving but tell me do you think I'm dumb I might be young but I ain't stupid" that means that he's trying to make up excuses but the girl knows he's lying