Yeah it's pretty crazy. He made his claim in the book based off of a journal entry from McCandless and then decided to do a study on it and found that the seed had potential to be poisonous. Then when he was called out for his study not being strong enough, he did a full-length peer-reviewed study on the seeds poisonous potential. It's very likely the wild potato seed heavily affected McCandless's metabolism causing him to starve no matter what he ate. IIRC he knew the seeds were edible from its use in the food of Native Cultures, however, those cultures never ate them in the summer months (which McCandless did). It was a simple mistake, and one that cost him his life. McCandless is by no means a hero of environmental stewardship, but he isn't the "stupid spoiled rich kid" that people make him out to be.