That should be interesting. He's got several questions to answer.
Why did he think that he had a medical exemption when
google could have told him in less than 90 seconds that he didn't?
Why did he then travel to Australia, knowing he had no legal right to enter?
Why did he lie on his visa?
And - pre-empting his likely answers on the above questions - why is he blaming others and not taking personal responsibility for his own travel documents?
Why did he think it a good idea to break isolation when he knew it was a legal requirement after he got a positive test result?
Did it ever cross his mind to make a stand on his vaccine-choice principles and not go to Australia?
I get the feeling that if he's just making a statement, and not facing questions, he'll make things worse for himself. And if he's facing friendly questions from a Serbian interrogator, it won't be much better, but it could be unintentionally funny...