I'm reasonably certain this trope has roots in reality, in as much as Gung Fu is thought of as "a way" or "an art" of doing something. Mastery of any set of skills is Kung Fu, whether it be for combat, practical purposes, or simply as a form of meditation. Since Calligraphy, Tai-chi, Archery, and Tea Ceremonies have all been described by Eastern philosophers as forms of meditation, this is doubly true.