Not to be argumentative but I found this on Google, which has the nuances your finding lacks.
"Cultural appropriation refers to the use of objects or elements of a non-dominant culture in a way that reinforces stereotypes or contributes to oppression and doesn't respect their original meaning or give credit to their source. It also includes the unauthorized use of parts of their culture (their dress, dance, etc.) without permission.1
In this way, cultural appropriation is a layered and nuanced phenomenon that many people may have trouble understanding and may not realize when they are doing it themselves.
It can be natural to merge and blend cultures as people from different backgrounds come together and interact. In fact, many wonderful inventions and creations have been born from the merging of such cultures (such as country music).
However, the line is drawn when a dominant cultural group makes use of elements of a non-dominant group in a way that the non-dominant group views as exploitative."
Cultural appropriation is more than just malicious representation of a culture, it can be anyone using elements from a culture that isn't theirs. It's not always bad, like no one cares if Bollywood or anime does it with Americans, or if some Mexicans out there use a cultural element from France for something. It's more scrutinized when a dominating culture appropriates one that's been exploited, and that's the most common, but any culture that takes elements from another is appropriating.
The whole topic is a grey area since taking anything from a culture, even tourist merch, can reinforce stereotypes of that culture. The OP making a story using an element from the American Indian culture, while not being part of that community themselves, IS appropriation. Is there anything wrong with that? Nope. They don't intend to do harm, they're doing research, it's not some "wtf" thing, so they're fine.