I think it is likely that there was no positive test at all. It all seems a bit coincidental that the only way an unvaxxed person without a medical condition could have gotten into Australia was via having a recent positive diagnosis and then Novak just happened to have a recent positive diagnosis. It's also suspicious that he has had a previous COVID infection. If there was no Omicron then I think this would be very suspect. Omicron makes it a lot less suspect because getting re-infected with this variant seems more likely and the base rate of infection seems to be higher.