Is Muslim an ethnic distinction?

The headline reads, "Pope baptizes Italy's most prominent Muslim", but in the article it says,

Allam was born a Muslim in Egypt, but was educated by Catholics and says he has never been a practicing Muslim.

So how can one be born a Muslim? I understand how someone could be born a Jew, yet not be a believer in Judaism (there is a ethnic group called "Jews" and a belief system called "Judaism". I know that many of the Muslims in the Middle East are of Arab descent, but I was unaware that there is an ethnic group called Muslims. Where did they come from and where are they most prominently living now? It seem like a big deal that this guy, Magdi Allam, converted to Catholicism and was baptized by the pope on Easter weekend, but he says he has NEVER BEEN A PRACTICING MUSLIM. So why is he fearful of his life? If a person is born a "Muslim", yet don't practice Islam, is that considered Islamic apostasy? The only why I can grasp this at this point is if Muslims are an ethnic people group like the Hebrews where during the times of the Old Testament. In those days, being born a Jew meant that you were born into the family of Yahweh and any movements contrary to the Mosaic Law were considered apostasy. However, I feel fairly comfortable saying that for Jews under the Mosaic Law, not practicing the Mosaic Law as akin to apostasy. I don't think the apostasy flag went up only after Jew's began worshipping other gods, I think the apostasy flag was flying high at the point when the Hebrew ceased to practice the Law. Given this, I'm struggling to understand the dynamics in play with brother Allam. I do believe dude is in danger and that some Muslim people are mad at him. I'm just trying to understand why?!?!?!