Nope, that's not what it means at all

Genetically linked behaviors follow distribution curves. There is always variation in every population for any behavior. When a behavior is highly selected for, alternative behaviors become more rare...but they still happen.

A good example of this is homosexuality, evolutionarily speaking this behavior is highly selected against (reduced babies). It still occurs in all sorts of species.

What this means is that around 2/3rds of humans are strictly monogamous. Around 1/3rd of humans are promiscuous or partially promiscuous. These are instinctual behaviors that can be overcome somewhat by cultural norms. On an individual basis, for every 3 people you meet, one instinctually finds sleeping around to be their "normal" behavior.