If you phoned the Brisbane office to purchase the ticket, then they were absolutely correct in that you have to pay the ex-Australia fare, however they were wrong in the description of why

If you have the ticket issued in a country other than that of the country of departure, then you have to pay the higher of the fares of country of issue and country of departure

Phoning AA in Brisbane, the ticket will be issued in Australia. Since the ex-Australia fare is higher than that of ex-NZ, the ex-Australia price applies

If you phone or visit AA in NZ, you should have no issues getting it issued at the NZ price

Dave