The meaning of disheveled hasn't changed much from the 16th and 17th centuries, when it referred to disordered clothing or hair. If he were coming in from the snow, you could blame static and hat-hair for his disheveled look, but no, he just never uses a comb.
People or things that are disheveled are kind of a mess. Wrinkled clothes, knotted hair, and a chaotic house might earn the adjective disheveled. There are a lot of synonyms for disheveled, including "disordered," "sloppy," and "cluttered." A person can look disheveled when getting up in the morning, and some people even adopt a disheveled look on purpose, trying to appear casual about grooming and dressing while working hard to achieve just the right unwashed and mussed-up style.