Usually, a resident alien residing in the U.S. is taxed with worldwide income.
However, based on the tax treaty signed between the U.S. and New Zealand, the income from the real estate property is reported to the State where the real property is located. That is, you should report income and income tax of the sale of that property to New Zealand.
The website link and citation are for your further reference.
Please feel free to follow up.
Fiona Chen, MPA, Ph.D., CPA, ABV, CFF, CITP
Income from Real Property
1. Income derived by a resident of a Contracting State from real property (including income from agriculture or forestry) situated in the other Contracting State may be taxed in that other State.
2. The term "real property" shall have the meaning which it has under the law of the Contracting State in which the property in question is situated. The term shall in any case include property accessory to real property, livestock and equipment used in agriculture and forestry, rights to which the provisions of general law respecting landed property apply, usufruct of real property and rights to variable or fixed payments as consideration for the working of, or the right to work, mineral deposits, sources and other natural resources, ships, boats and aircraft shall not
be regarded as real property.
3. The provisions of paragraph 1 shall apply to income derived from the direct use, letting, subletting or use in any other form of real property.
4. The provisions of paragraphs 1 and 3 shall also apply to the income from real property of an enterprise and to income from real property used for the performance of independent personal services.