This is actually right, read the requirments to become pope, there stand nothing that you have to be a christ.
If i remember right, "by the decree of God and of His Church, by the testimony of nearly all the clergy, by the college of aged bishops (sacerdotum), and of good men." means only, that in the conclave you can become pope, when you get 2/3 of the voter behind you. Important fact, the rule that the person has to be a Cardinals can be overwriten by the decree of God.
So if you are the son of god and sunni, god himself will give the cardinals the hint and they will vote the son of god. Pope is actually the only position in holy catholic church, where gender, religion, historical background and so on can be overwriten by the voting rules.