So, ON isn't a foreign operator because they operate VH aircraft? And in any case, INU is over the PER nowadays flying for XR, although I am sure that RON could probably have been used at short notice.
At the end of the day, Air NZ will do whatever they think is best in the circumstances. For whatever reason, they chose to bring in one of their own and wear the anger of the pax rather than chartering a replacement. Heck, they probably had the option to borrow a bird from DJ to operate it but chose not to. I am sure there are reasons for that.
At the end of the day, the service ran, pax got there late but nobody died and safety was maintained. Good outcome I would have to say.