Just done a quick bit of research, and as I suspected:
Melbourne Activist Legal Support (MALS) expresses concern regarding the failure of police to act compatibly with human rights and give proper consideration to human rights in tactical decisions whilst policing opposing rallies at Parliament House on Saturday, 18 March 2023.
mals.au
Antifascists wanting to remove the nazis from Parker's rally would have had to get through this lot in order to do so:
View attachment 377121
That being the case, I don't think that you can really conclude that "antifascists were happy for there to be people seig heiling in their community" just because they failed to remove the sieg heilers on this occasion.