Even in my world, there are those who have very different ideas about what demons are like. They and the ones who deal with them are widely misunderstood. It's possible either your friend comes from a world with vastly different rules regarding demon contracts, or they too are simply uninformed.

[He figures it's a mix of both, probably -- but hopefully they're just some religious fanatic and not an exorcist, or else he'll have to be more careful when appearing around Yona's friends.]