I posted from the article that they didn't respond to several questions:

X's noncompliance was more serious, the regulator said, including failure to answer questions about how long it took to respond to reports of child abuse, steps it took to detect child abuse in livestreams and its numbers of content moderation, safety and public policy staff.

I speculated that probably they also need adequate responses, but that's not what the article or the fine is about.

If one of the individual sites in the Fediverse was asked by Australian regulators, I bet they'd respond fully. It's not quite the same situation as Twitter, either - none of these sites are large enough to require many staff members, and don't have their own live streaming platform.