I know this is mn so RTFT is unlikely, nevermind an article in a link but this does not suggest a failure of the NZ approach. The people were not necessarily Brits. They did not attend a funeral.
There was an error in how they were questioned, which, had it been done properly would probably have resulted in a test and they wouldn't have been allowed to then travel to Wellington. They did travel from the UK, but via Doha and Brisbane. It can't be known they had The virus in the UK. They then had contact with various airport staff etc. but only one other family member plus the deceased.
The article is very calm and measured as is the response from the NZ authorities.
Personally, I don't think they locked down too early, and I think the death stats prove that, but I agree they'll have a tough time in the future as the economy gets harder hit and it's unrealistic to get tourists to quarantine for two weeks. But with Australia being the biggest source of tourists, the bubble could be the stop gap before the vaccine.
Sorry I've gone on a bit!