The Case for Sasquatch by Bob Gymlan

[Byrd]

Perhaps a reality that once was grew into mythology and folklore. The old wild man of the woods representing our last interaction with neanderthals.

I would think it was more likely to be based on "feral children"... basically the nonverbal autistic.  The stories of the "last Neanderthal" were not something that would have been known by the world, but rather by a small band of people (30? 50?  Fewer?) who met them.  That's a tiny story and not one that would survive in the noise that came from those who survived.

Sasquatch mythos seems to be largely European in origin: https://en.wikipedia.org/wiki/Bigfoot