Here we get into the weeds of what constitutes a true believer. If a guy was raised in a Catholic home, but cared nothing about the faith, never went to church, never read anything related to religion, and is an active criminal, gets caught, and on his induction forms for prison says he is a Catholic, is he ? I doubt few folks like this would believe themselves atheists, though practically they are.
If the same guy, for fun, joins a Catholic study group in prison, and is truly converted, studies, takes part, goes to mass, and truly believes, he really is a Catholic.
Back in my atheist days, my first job app after college had the religion question asked ( it was legal then).
Because my family was Southern Baptist for generations, I quickly wrote Baptist without even thinking about it.
Yet I rejected Christianity, warned my family to never bring it up in my presence, basked in the warmth of macro evolution, and scoffed at believers, etc., etc.
I was a familial ,in name only , Baptist. If I had been popped for something that required a prison term, would I have entered prison as a real Baptist ?