1. He thinks this girl is stupid. She can only do things and get along with others. She is inferior to others in IQ and language.
He may just say it casually. Maybe a man and a woman are close, so they always call him this way, which makes them more familiar and closer, because it is impossible to call them strangers like this.
3. If a man thinks that a girl is cuter, and then he is stupid in MengMeng, it is not that he is really stupid, but that he is simple and lovely, and has no scheming, which makes people like him very much.