Good catch. No such fallacy exists. Contextually, the implied reasoning (though faulty) relies on the fallacy of denying the antecedent. The mons ponus - if A then B - does NOT imply not A then not B. So if you see B, that doesn't mean A any more than not seeing A means not B. It's the difference between a necessary and sufficient condition - A is a sufficient condition for B, but the mons ponus alone is not sufficient for determining whether either A or B is a necessary condition of the other.