I love that both Turnbull (who will be the internet minister) and Abbott (who will be prime minister) are both back pedalling saying they didn't have time to read it properly.
No, it's just about having something you can point to when a pesky journalist is making too many questions: "oh, it's all in the manifesto|whitepaper, please look it up". Those docs are written by unpaid interns and forgotten a minute after ballot boxes close.
If I recall, there was a blurb on it a few months ago--it's neither opt-in or opt-out, but forced-choice (you can't start using your connection until answer a form stating whether you want it filtered or not.) The party pushing it was just asking for it to be marketed as opt-out ("default yes"), since of the two radio buttons, the "yes" option would be the checked="checked" one.
http://www.abc.net.au/news/2013-09-05/no-internet-filter-say...
Though in reality we still have the AMCA filter, which has been used badly in the past.