Counted as affiliation of by culture ,studies are as said not a census. I was born into something . My belief may be something else. Then also not all religions are equal in my book . The desert variations are at one end. Others Sikhs , Buddhism, variations of different polytheists and are more on the other end...
One end is more prone to blow shit up just for who beliefs in what skydaddy.
Am I religious? No . Am I spiritual? sure but I would never trust a hippie. And my worldview is more based around material reality than idealistic wishing. Where do I end up in the stats?