Medieval critics debated what predating Muhammad by Islam meant

Evidence

Ricoldo seems to have understood the Qur’anic position, although he subjected it to petty and pedantic arguments: Neither can the Muslims say that Abraham and Noe are Muslims because Muslims are descended from them; for this interpretation is contrary to the Qur’an, where it says that Abraham was not a Christian and was not a Jew, but a pure Muslim. — Norman Daniel, Islam and the West, 166