While it's unfortunate it's something people need to research before booking flights. Most *A airlines have booking classes that won't offer any form of mileage or status credits to *A using anything but their own programs.

You can't expect the airline issuing the ticket (Air NZ in this case) to be an expert when it comes to understanding United's FF program. Likewise if I book an Air Canada or Lufthansa flight (both of which are examples of *A airlines who have numerous booking classes that don't offer any APD or SP to Air NZ customers), I wouldn't expect Air Canada or Lufthansa to know answers to questions.