Nyet. The proper follow-up is to ask if he is of Catholic background or from a Catholic family, even if that may offend. A former Catholic is more Catholic than a Muslim. Simple as.
Auguste Comte, an atheist, was still a papist in meaningful ways. A Frenchie from a Catholic culture whose worldview was 'Catholicism without the Pope or religion'
https://en.wikipedia.org/wiki/Religion_of_Humanity#Similar could be said about Stalin and Orthodoxy. It's also been said Barack Obama is somewhat 'culturally Muslim' - and for pretty good reason when you look at his background.
https://www.upgoat.net/viewpost?postid=681cf77cd122e&commentid=681d1b078565fThe above taken from the above thread.
An Estonian atheist is not an Irish atheist is not an Iranian atheist.
As Sartre, an atheist, said: in reality we are still Christians. Cultural Christians as Richard Spencer, another atheist, put it. A Christian atheist's rejection of religion is not even the same as a Jewish atheist's is, nor do they see the world the same way. And an atheist of Muslim background?
There doesn't seem to be anything here yet