From the kiwibank Airpoints card T&Cs:
∙ Interest will be charged on any cash advance or balance transfer
from the date the advance or transfer is made until the date it is
repaid in full, except where stated otherwise in any specific terms
that we publish as part of any applicable promotion or special
offer. Cash-like transactions, such as the purchase of gambling
chips or foreign cash, are treated as cash advances
I can't see any reason why the purchase of Airpoints Dollars would be treated any different from gambling chips. Both are effectively cash equivalents.