In my view, we all get to choose. Statistics NZ gives guidence, as the question is raised with the regular census:

Statistics about ethnicity give information by the ethnic groups that people identify with or feel they belong to.

Ethnicity is a measure of cultural affiliation. It is not a measure of race, ancestry, nationality, or citizenship. Ethnicity is self perceived and people can belong to more than one ethnic group.

An ethnic group is made up of people who have some or all of the following characteristics:

• a common proper name
• one or more elements of common culture, for example religion, customs, or language
• unique community of interests, feelings, and actions
• a shared sense of common origins or ancestry, and
• a common geographic origin.

It is my view that a person can change their ethnicity over time. Also, belong to more than one.

According to my DNA I am mixed. My greatest affiliation is based on geography, and secondary to that, the peoples that populate the regions I feel connected to.

Mostly, I feel like a citizen of the planet, and interact regularly with people from a lot of places. I am currently based in Auckland, NZ, where over 40% of it's population was born in another country, and according to recent censuses, over 220 ethnicities are represented. This makes Auckland wine of the most diverse populations on earth. Sitting in a public hot pool this morning, I was the only European looking guy, with one African and the balance made up of Asian Han, Malay, Indian) and multiple Pacific looking peoples. Multiple languages were being spoken. I recognized Chinese and Samoan (I think).

Bottom line, is that you get to choose.