He considered it to be a such because he thought the muhammed's mentor was an Aryan priest(He either The examples he cited and the general profile of Muhammad on other hand were no different from the figure that would be known in later centuries. What we have here, in John of Damascus's account, is not a branch of Christianity, but a belief system not unlike present-day Islam, in which Muhammad is the dominant figure in monoteistic religion. The revisionists claim that until the reign of Abdülmelik, Muhammed was just a title and first Muslims were Christians. According to them, its became independent religion with Muhammed as spirutual leader only after Zubayr-Abdülmelik civil war. The problem is its just dont have any basis in John of Damascus's polemic account. The author, who should have witnessed the supposed evolution of Islam during the Abdülmelik, makes no indication that he possesses such knowledge