Allow me to offend everyone at once. Jesus didn't come from a man at all, but the Holy Spirit, according to the gospels. Salvation doesn't come from a man, but from God, through Jesus as the final blood sacrifice. So technically, if he was Jewish, then Islam got what they wanted, a dead Jew, and if he was Muslim, then the Jews got what they wanted, a dead descendant of Ishmael (and/or false prophet/Messiah). Either way, while neither side is correct, everyone got what they didn't deserve, a way to access the Father and atonement for sin.