Then how can Islam say that Jesus was not divinty, truly God and truly man?
Jesus was no ordinary man, or ordinary prophet.People sometimes miscontrue the usuage of the word prophet to mean some kind of pagan Greek oracle. To Muslims, a PROPHET is the Sign of God on Earth. We believe Jesus was "the Infallible, the Immaculate Prophet". Like Moses, God gave him power beyond all men.
As far as his divinity is concerned, Muslims are taught that Divinity is the sole province of God, the Almighty Creator (to you, God the Father) You know that part of the Old Testament, where it says something to the effect "For the Lord, thy God, is a jealous God" (and so on). Plus, there is the commandment "Thou shalt not have any gods before Me".