Rather than referring people to press releases and news articles, it is best to look at the specific Warning Letter itself. Not a "ruling," simply restates long-standing practice.

https://www.transportation.gov/sites...3%202020_0.pdf

These DOT rules apply to all US carriers and to non-US carriers for flights or from the US. In OP's specific situation, the DOT rule applies to NZ for a departure from LAX.

To be clear, the Warning Letter is not new in the least. These rules have been in effect for many years. The Warning Letter simply advises carriers that if they have wrongfully denied a refund, in light of the Covic-19 emergency, they will not face an enforcement action if they promptly issue the refund.