The stated validity is residency not nationality so by that you should buy Eurail.
However as your passport does not match the country that will be listed on the pass you would need some documentation to show your NZ residence should anyone question you.
Even though it does contradict the residency rule you could get and use an Interrail with your Dutch passport, you wouldn’t get any questioning of that as it would match.
The only material difference between the 2 prodcucts is that Interrail has restrictions on use in “home” country. Were you to buy Interrail you would only be able to travel in Netherlands for 2 days out of the overall pass validity.