Because he submitted to Allah and professed there is only one God worthy of worship

Muslims believes all prophets like Musa (Moses) Daud (David) Ibrahim, Ishak (Isaac) etc preaches in believing only one God (not in human form like some other religion). Muslims are only a name for the followers of Muhammad SAW. Jesus is a Jewish that also follows the teaching of Moses that believes in one God like Muslims

Muslim just means someone who submits to god and only god so ya he’s Muslim by definition

Islam is the only religion that reconciles all Abrahamic faiths as a true religion should. Look at most comments from so called Christians and Jews in this thread, spewing hatred. Most of these commenters don't know a lick about Islam and are mostly talking about points from mainstream media.