The first line of defense if somebody accuses the author of cultural appropriation is to simply reply that it is his own culture. It's odd to presume that he has any special requirement to justify his use of a word that he, as a New Zealander, has as much right to as anybody else.
Te Reo is often considered a taonga due to its value in the heritage and identity of the Māori people of New Zealand.
Te Reo names are often gifted by Iwis or individuals with sufficient Mana. As a Tangata Whenua Inia, I was strongly recommended to avoid using Te Reo names in business due to cultural reasons.
I'm from New Zealand myself, I understand the cultural context here. I grew up using the word Kākāpō as the common word for referring to the actual bird. If I was the author, and somebody takes offense from my usage of the word Kākāpō (the word used in English as well as Māori), I would politely ignore their concern. Mana, just as in World of Warcraft as in real life, is of little concern to me.
And getting precious over a word is ridiculous, it seemed to be a common theme growing up in NZ, there's a general apathy until there's some perceived benefit and then suddenly it's about race and culture.
