I just think they're picturing the classic popular kid from movies that is there just to bully the protagonist, in reality (or at least from my experience) popular people are usually really easygoing and it's very nice to be besides them, and usually they are good hearted too!

I have encountered the "popular" kind from movies and besides their close group of screwups, usually people stay away from them, I don't know if this applies also to high schools in america though but if someone's bullied another person for being a nerd usually it's the "nerd" that made new friends that day while the perpetrator got more isolated from the rest of the class