Yeah, the "ka" 家 in "mangaka" is the character for "home", also commonly used to signify an artist. This usage might have stemmed from the idea that an artist is a person who works his craft in his own home, but who knows... They have several of these for people of different skill sets, for example: "sha" 者, which is used for jobs that, i guess, require a great amount of dedication, concentration and accuracy, such as "isha" 医者 which means "doctor", or "ninja" 忍者 which means "juggalo"; "in" 員 which is used for the most regular of jobs, office jobs, such as "kaishain" 会社員 which means "company employee".