A claim of infringement has nothing to do with the defendant’s own IP, but rather the IP of the claiming party. Infringement is the result of a business activity. Holding an IP right (patent, copyright, trademark) doesn’t protect you from infringing on someone else’s IP, nor does lack of IP rights indicate that you can’t infringe. IP rights often overlap and rarely cover an entire product or process. Sometimes patents are granted to different parties for the same thing, and there are cases where an awarded patent will later be invalidated.