It wasn't grass pea - the author of the article was making a comparison between the symptoms of ODAP poisoning in people who had consumed grass pea and the symptoms displayed by McCandless. The plant that he was eating was wild potato, not grass pea, and it was McCandless's death that motivated some researchers to examine the wild potato plant to see if it contained the same toxin; that toxin turned out to be present in the plant, which had not previously been known.

According to the article, McCandless was using a reference book to determine which plants were safe to eat; the book listed wild potato as non-toxic, because it was not yet understood that it contained ODAP. If it had been known, McCandless would not likely have eaten wild potato, would not have been poisoned, and would likely not have died in the way that he did.