I took it to mean there may have been multiple disagreements with the constabulary while in Australia so while he was deported for something in one state there could have been an outstanding matter in another. I can also see a circumstance where he’s met and married a New Zealander in the UK in the intervening years so right now can enter NZ, would like to do so (half the UK would probably like to do so right at the moment) and can’t do so without transiting Australia. Starts all getting a bit far fetched but that all fits.

My take is similar to many of the others, the real issue would be entering NZ, not transiting Aus, so if you can get into NZ then it shouldn’t be an issue.