What does Junior mean when he says something is "absolutely tribal" on page 89 of The Absolutely True Diary of a Part-Time Indian?

On page 89 of The Absolutely True Diary of a Part-Time Indian, Junior says, "We [our family] are absolutely tribal." Junior makes this statement after his mother reveals that his older sister Mary married and moved to Montana to live on another reservation. By saying "absolutely tribal," Junior refers to the history of his family and their life on the Spokane Reservation. Junior says both his mother and his father have only lived within two miles of where they were born and that his grandmother only lives one mile from where she was born. No one in Junior's family has ever left the reservation. He says, "We Spirits stay in one place" (89). The Spirit family has an affinity to the reservation, so they stay to be near their other family members and other members of their tribe. Mary leaving the reservation is a huge deal to the Spirit family, who for generations have remained together on the Spokane Reservation.