They controlled for diet, natural feeding tendencies, etc. presumably to match conditions in the wild. They never said the monkeys who "naturally" ate the most

They controlled for diet, natural feeding tendencies, etc. presumably to match conditions in the wild. They never said the monkeys who "naturally" ate the most DIDN'T die first; they probably did. But that certainly doesn't mean that calorie restriction below the "average" feeding tendency doesn't provide benefit.