As ridiculous as these question may sound, gotta put it out there...
Who owns the airspace above Norfolk where NGA circled?
Australia or New Zealand?
Australia.
Norfolk Island is part of Australia.
The airspace above Norfolk Island, and out to 12 nautical miles from the territorial sea baseline, is part of Australia.
I may be completely wrong, but I think that in the course of the AAI there was discussion of an arrangement between Australia and NZ for NZ to administer that airspace on behalf of Australia. But whatever the case, the airspace is owned by Australia.
Again, I may be completely wrong, but my fuzzy recollection is that during the AAI, forecasts for YSNF magically re-appeared on Australian Area forecasts. After all, the 'Y" in YSNF = Australia and the "S" = the erstwhile Sydney FIR.
Judging by news reports, the government of Norfolk Island is a bit of a basket case. They want to be self-governing like the Northern Territory, but don't have the revenue to discharge those responsibilities properly. I imagine - again, I could be completely wrong - that the whole schemozzle became 'too hard' for Airservices Australia, but the AAI 'encouraged' Airservices Australia to try harder...