A derivative metaphor (tab'iyya) is expressed through a verb, derived noun, or particle. It is conventionally explained by analyzing a comparison at the level of the underlying source meaning, then tracing that transfer into the derived form.
The literal verb «رَكِبَ» means to ride. In «رَكِبَ كَتِفَيْ غَيْرِهِ», it conveys clinging to or pressing another person with unusual persistence, borrowing the idea of mounting.
A sentence does not become tab'iyya merely by containing a verb; the verb’s meaning must actually be transferred.