The article indicates that the non-religious have a higher percentage of people intending to vote yes. But will that equate to a higher volume of people total? I went and looked it up from the 2016 census.

• There are aproximately 24 million Australians. ^LINK
• Christians make up 52% of that, but only 22.6% of our population are Catholic. ^LINK
• 30% of our population reported no religion. ^LINK
• 79% of non-believers polled intended to vote yes (OP article).
• Catholics and non-Christian religions were more likely to support same-sex marriage, with two thirds of both those groups indicating they were in favour. (OP article)

Their are around 5 million Catholics in Australia and the majority of those polled were the biggest backers from their own group, but not overall within our population total.

It should also be noted that some households may have self reported erroneously out of concerns for privacy. I've no measure of the frequency that may have happened or how it might change my conclusions.