I cannot see this happening in reverse--can you? Christianity is the only religion in which one does not save himself through works or become a god.
It is true that Judaism, Christianity, and Islam have the same roots. Deception could have been avoided by summing it up in just a few sentences: Jews believe in the Old Testament, Christians believe in the Old and New Testament, Muslims believe in a Pentateuch that they twisted to make Ishmael the chosen son instead of Isaac. The Pentateuch says Ishmael was a "wild ass of a man" who would live in hostility toward all his brothers--which we clearly see in his Arab descendants as a whole.
Muslims believe in conversion by politics--they want to conquer land and take over countries and rule by a "convert or die" policy. If you don't understand this, you need to do your research. Christians have done horrible things and there is call to violence in the Bible, but as a whole, Christianity is not religion that preaches the same principles as Islam WHATSOEVER.
Unfortunately, this man who is not strong in his faith is reflecting both American Christians and Muslims in that they have really no idea what they believe. But there are Muslims who do know and aren't going to tell an infidel just like there are many Christians who are too pansy to tell you they believe you're going to hell if you don't believe Jesus is God.