What was this Creature?

[BIAD]

hmm, let's look at the circumstantial facts...

It threw rocks.
It chased them.
It was BIG, towering 6 feet above him.
It seemed to have the ability to disappear or "cloak" at the reedbeds.
and... it wasn't actually spotted on the experimental forest facility... it was in the remote woods on the ridge near that facility.

My money's on Bigfoot.
All of the stated facts seem to match many of the commonest reported traits observed in Bigfoot encounters.

That's what I'd go with too, Gordi. But the possible subject doesn't fit the narrative of the television show!
So they angle a 'description' and push the 'Military Forces are secretive' idea.