Obviously, you fail to understand that expression.
Ever heard of "Proving Grounds" or the like? It means that you're testing the rule...the exception tests the rule and shows that it isn't a rule.
The rule is, primate eating patterns are herbivorous. The exceptions are, a few species that have omnivorous patterns. The fact is, humans are closer to primates in anatomy.
The fallcy is in the article,” We’re a carnivorous species - our gut is identical to that of a big cat.”. The trap is, freepers who buy into that argument to justify carnivorous patterns in humans.