It’s certainly a good case to test both the breadth and the strength of that right in Australia.
That said, as far as I’m aware we actually don’t have a a right to ‘freedom of speech’ in Australia. Yes, we talk about it a lot but it’s a US concept that we’ve imported into political discussion. The courts here have given some expression to it in the implied right to political communication.
Does Folau’s tweet fall attract the protection of that implied right? Hard to say, I reckon. Arguably not but it depends on how widely the court is prepared to interpret ‘political communication’.