I recently fly AKL -> SFO on NZ8. Flight was ticketed via United. It was Business and the booking code was (P).

I received 28 Status points. on the Air NZ website P code with United maps to deep-discounted economy fare - thus on this basis it has been credited correctly.

My (basic) understanding is if you fly on NZ metal even with a United ticket you are eligible for the same earn as if booked on NZ ticket ?

Questions
1) Is this correct?
2) Why would a Business Class (non discounted) fare earn the very lowest earn?

Any insight appreciated.