Why wouldn't they call the local CASA FOI and say "We're having a fly-in, expect a lot of aircraft, should be a fair bit of congestion on the area freq so how about we use an alternative frequency, we suggest 126.7."
That would have been smart, and to not do so is either showing lack of foresight, or an intention to deliberately overload the frequency in order to highlight the issue. You wouldn't have had anything to do with it I suppose?
Edit: Sorry Aussie Bob, I replied about half a second after you did. If CASA refused to be sensible about it, well fair enough, they're in the wrong.