DY: It wouldn’t apply to an Eved K’na’ani either, I assume. A person might have a Kinyan on the E”K but he is not fully “his” in the sense that he has absolute R’shus over him. The “human being-ness”, for lack of a better term, of the E”K still belongs to himself (on a related note, see the Sugya in Gittin about a person who is Mafkir his E”K but died before giving a Shtar Shichrur), which is why the Adon cannot permanently damage him.
See also Chullin 40a for a related topic.