Hey
@firedragon
You might have already got an answer on that question, but I can summarise for you.
Every 4 years or so, we do a census. Each household has to respond to a series of questions. Where children are involved, there are still questions to answer. If someone is staying over at your house that night, they would respond on your census rather than their own.
So it's basically a giant survey.
In typical Australian fashion, a few years back lots of people listed their religion as 'Jedi', since there was an urban myth that it would be recognised as a 'real' religion if 50k people listed it. Don't ask me what a 'real' religion is.
But in response to your point, no religion just means 'no religion'. You could absolutely be an atheist and put that, but you could be an agnostic, or spiritual, etc in many different ways.
It's really a measure of adherence to religion...but people being people, they keep tying it to a measure of belief.