I might be a little unsympathetic to the buyer since he's, well, not a Kiwi.
He has to have citizenship or a residence class visa to purchase residential property.
So if he was eligible to buy they house he's pretty much as "kiwi" as most people around here...
If he didn't have PR then this is what may have tripped everything up,
Do Real Estate agents check this on offers? or is it simply assumed that purchasers understand the rules?