Concept Of Ummah And Superiority Of The Prophets
True! All the true followers of the prophets of their times were Muslims.
Because of the elevated status of the ummah of Rasool ul Allah (saw) in particular. And especially because of the notion that the ummah present at the time of Rasool (saw) and the later ones to come are especially blessed because of him. I heard a scholar saying “it is Allah’s Ahsan on us that we are from the ummah of Rasool (saw).”