Unless you are on a ticket that includes north america a total checked baggage allowance of 20kgs for non *G travelling in economy is fairly common (certainly not limited to NZ). So you should only have been charged for 9kgs, but since not charged at all that is even better.

As for carry-on limits, both NZ and QF enforce much more than US carriers. Although generally not as strict on business/elite pax as economy.