It was actually quite tame. It was basically like the Odyssey where he gets captured and is accounting on how he survived and found his way home.
Whether if it's Historically accurate is up for debate. But there's not a lot of material on that subject let alone first hand accounts. So you both have to accept, and deny his opinion on native cannabilism in Brazil.
That being said it's a narrative, and it doesn't really add any insight or reasoning for why the practice of cannabilism. Some theorize that it's a form of ritual sacrifice similar to the holy eucharist in Christianity. Other Historians suggest its an anti colonialism because most of the sacrifices were people who enslaved the natives and were therefore enemies.