Quote from the source you cite:
“New Zealand may not be a socialist country, but the welfare system in the country is very wide ranging.”
So you have a line between the welfare state level and socialism?
What income is taxable in New Zealand
New Zealand taxes income on both a residency and a source basis.
New Zealand residents
If you are a resident of New Zealand for tax purposes, you will be taxed in New Zealand on all of your “worldwide income”. This is income derived from New Zealand as well as income derived from all other countries.
Find out about your personal tax residency status
Note
Your worldwide income includes any income that you derive in a foreign country even if you do not bring the money into New Zealand. For example, your worldwide income could include:
•an amount of interest you derive from funds you have in an offshore bank account
•rental income
•salary and wages paid both by New Zealand companies and offshore companies
•foreign pensions - find out more
https://www.ird.govt.nz/international/comingleaving/coming/payingtax/