It’s worth noting that the book does contain several chapters which, on their own, would probably be classified as “historical fiction”.
They are clearly identified by the title “When Life Was Our Own”, and the author introduces them as a story which will provide context and depth for the surrounding non-fiction text.
A pretty reasonable approach for a children’s book, and also one which is thematically appropriate, given the importance of oral history in the preservation of Native American culture.
The book starts with a story, "When Life Was Our Own," which describes Wampanoag life before any European contact. The story was created to re- late traditional Wampanoag culture, beliefs, prac- tices, and values based on our oral traditions and research done over many years. There are no writ- ten sources of these early times, due to the processes of colonization described in the other parts of the book. An understanding of precontact life brings clarity to the impacts of colonization on Indigenous people.
Truth is a constuct.