I think person B is saying it in a tongue-in-cheek way, as a joke, because it's not possible to know if someone is rude just by knowing they have sideburns. Maybe they are just teasing person A, or making fun of person C.
It's also possible that person B actually means to say "he has attitude" (without "an"). This changes the meaning. It means he is flamboyant, outgoing, stylish, making a statement, like an artist who uses bold colours. He might still disturb a snowflake, but most people won't mind - some people will even admire him.