Going to start the caveat that I don’t think he should be in Australia in the first place. The (federal) government are perfectly entitled to set what ever rules they want to.
But….
I think it’s important that everybody knows what the rules are. In this case my understanding is the federal government delegated admissions to the the state government (Victoria) who said okey-dokey in you come. And he the got a plane and the federal government decided they didn’t like it. I don’t like it when governments suddenly about turn like that. It’s just not cricket (no pun intended). If he’d broken any laws whilst in the country, or there where material changes in circumstances then fair enough kick him what but actually changed (other than the public outrage) between him being told he was in and his arrival.
He’s going to loose in the first round anyway after all this. Sod’s law ain’t it.