This is a difficult question that I've actually been trying to come to terms with for the past 2+ months (well before I noticed this poll right not). If I had seen this poll mid 2021, maybe even Q3 of '21, I'd have easily answered with the "nonreligious (secular/agnostic/atheist) option. And that answer would've held true going back the past half a decade or more.
The problem is, that isn't really an accurate summation of my present day situation anymore. Because it's entirely possible for people to be "religious" while simultaneously identifying as "agnostic and/or apistevist and/or atheist". Case in point:
Confucianism
or Daoism
the Bahaii faith
Some sects of Buddhism as well (such as the Theravada, for instance) lack belief in any deities in the traditional Western sense (the Buddha was not a god, although stories of his life often have supernatural aspects).
Some traditional schools of Hinduism, such as Carvaka, Mimamsa and Samkhya, are generally compatible with atheism.
LaVeyan Satanists almost exclusively deny the existence of God, although it's a very tongue-in-cheek religion.
Then there are the Raelians who take the Bible and the Quran and the Torah super seriously... they just attribute it all to ancient aliens rather than divine wisdom.
And so on and so forth (and there are several others besides) each of these could serve as an adequate example of a non-theistic religion.
For the sake of full transparency: I'm an unbeliever, but I recently realized that my disbelief doesn't necessarily preclude me from returning to church, i.e. I'm not a "devout Christian" so much as a "cultural Christian" who continues to attend with, participates in and contributes back to the group - but more for the pragmatic and practical mental-health benefits afforded by being an active part of the social community rather than being caught up in adhering to all the spiritual teachings and ritualistic aspects of biblical theology within christendom
(although, with that being said, I do voluntarily meet with my pastor on a weekly basis -- outside of the regular Sunday service -- wherein we engage in thought provoking dialogues that explore various concepts such as faith, belief, knowledge, truth, history, science, psychology, etc etc. I remain deconverted to this day, but they're fun convos all the same, for sure!)
Idk. This is probably a lot more in-depth answer than you bargained for lol. TL;DR version is just that, sure, I'd agree that atheism isn't a religion (any more than theism could be considered a religion by anyone). However, while the top-level category-labels of "a/theist" doesn't in and of itself entail religiosity, it doesn't necessarily preclude identification with any number of religions that could fall under those umbrella-terms either ¯_(ツ)_/¯
To make matters even more complicated, in my particular case, I didn't opt for one of those non-theistic religions I mentioned above. Rather, I've decided to become involved with a monotheistic religion -- while still very much seeing myself as an agnostic/apistevist/atheist 🤣 but that's just the background I came from so it just happened to be the most convenient choice to make ¯_( ͡° ͜ʖ ͡°)_/¯
Idk if I'll stick with it long-term, but for the time being, feeling a sense of belonging (with the palpably present people in the pews -- not talking about holy "ghosts" haunting my "soul" as such, nor buying into a divine "spirit" acting as an all-seeing supernatural specter per se -- just practicing being present with another person) is doing wonders for my mental-state and well-being after such a long period of social isolation.
