But the government would discredit him if he were a spy. We can't take any of this at face value. The guy could also be intentionally planted as a disinfo agent to feed false information and see how Australia responds. The CCP discrediting him will add to this illusion. Or he could be a genuine scammer and liar. This also works.
What is truly unlikely is him being a spy. Since CCP is supposedly capable of performing murder on foreign soil (like every other major country is capable of) then what makes him so safe even if he is under watch for now? How about friends and family? I doubt CCP will bother to question anyone except direct relatives and even for a defector, not sure if these "Communist regimes" actually still take the lives of the relatives of defectors. Victor Belenko's family weren't touched if I recall correctly. There were another set of Soviet spies who defected to Australia in the past I think and their families were reunited after the Soviet Union went kaput. Can't say that's true for North Korea though but since defectors are plenty, you'd think they'd have a think about family especially east asian ones.
I'm going to go with liar, double agent, or western shill planted to create a narrative of China's supposed "takeover" of Australian politics and economy. CCP trying to insert influence is a sure thing and has been happening for years, but calling it a takeover is fear mongering. Key word here is trying. Trying and failing because it's not that easy for an obvious foreigner to be pulling the strings anywhere without overpaying and benefiting the local power holders anyway.
If he really is a spy, he would only defect to the Australians IF he had some high value intelligence information to give. That's his bargaining chip for getting accepted by the Aussies, instead of thrown into jail for being a spy. Now, this is the main point: if the Aussies really got some high level info from this guy, they would most likely keep every secret in order not to alert the Chinese Government and intelligence agency. This is because modern espionage operations all have contingency plans and mechanism. These operations are built and designed this way, because every agent is treated both as an asset and a liability.
This is why if this guys is real, the Aussie will make sure that the whole thing is kept in secret in order not to trigger the contingency plan/mechanism of the Chinese intelligence operations, all the while the Aussie (and its allies') intelligence operations would be able secretly run anti-espionage and counter-intelligence operation to capitalize on the intelligence offered by this guy. To publicly announce this guy's identity in mass media would be foolish, because this is simply not how intelligence work is handled.
In fact, if this guys is a real Chinese agent and a defector. The best thing the Aussie wants out of him would be to have him work as a double agent, without his cover being blown. This way, they could both get whatever intelligence he could offer now, as well as having him as continue as an asset (intelligence source), which could continue to get Chinese intelligence out of him. This is why, real defection are almost never publicly known. The public will be the last to know. By the time the public knows it, the guy will have no more value in intelligence work. We all know what would happen to an agent once he has lost all his usefulness.