CASA Manual says
"Fly-in, Competition or Cross country event:
A gathering of aircraft at an event or competition not on the basis of a general public invitation (A club event where no invitation is made to the general public [[similar clubs or groups exempted]) does not need to apply for an air display approval from CASA. CASA recommends that the safety management and third party considerations are followed."
Nothing to see here people, but I still would not be shouting my intentions to run a fly-in too loudly, because they do have every right to show up on the day.
Reminds me of the time a CASA FOI took a close interest in my little Sonex at a fly-in. Noting the lack of equipment on board he casually asked how I navigated. I pulled out my trusty motorcycle atlas, complete with pencilled-in tracks and distances. He thought I was joking but truth is that is exactly what I used. I found it a whole lot more comforting to know where all the roads and country pubs were than information offered by any 'official' aviation publication.