I'm (sadly) not a Kiwi nor based in NZ, but I don't think NZ have even started the vaccination process, nor are they even in a rush to do so.
Their borders are effectively closed, and any new arrivals have to go into a quarantine hotel on arrival. This of course means they catch people who are positive during this enforced 14 day isolation period (some flights are still entering the country) I think anyone who is positive isn't released until they can produce a negative test.
I believe they currently have something like 80 active cases, all of which are in quarantine rather than in the community, which means they can hold events like this without having to take precautions. Kinda hard for us to get our collective heads around but COVID just isn't a thing over in New Zealand. Kiwi's can't travel anywhere but life is pretty much normal over there by all accounts. We're a million miles away from being able to hold an event with 20,000 people attending.
Seems like they might be tightening their border controls even further, and you can't blame them. They can see all the chaos COVID and it's variants continue to cause across the world, so it makes perfect sense to keep a lid on the situation when they have it effectively completely under control.
New Zealand Further Tightens Border Measures to Combat Virus - Bloomberg