The majority of Australians are secular. Take me: I'm from a family that's Church-of-England (C of E). I've been an atheist since at least 10 years old (first strong memory of it), yet the first time I filled out a census form, I ticked C of E because that was my family's religion. These days the religion question on the census form is the only contentious one on it, because of things just like this. Lots of people associate with a given religion but don't really practice it - churches in Australia are fighting falling attendance and graying congregations.