Your question is a good one in recognizing the importance of these cultural artifacts and their strangeness, and the possible relationship to the Anunnaki given the larger‑than‑human bones that are otherwise human in makeup. These, indeed, represent beings of true Anunnaki as well as the Nephilim hybrid beings produced by mating of Anunnaki with human females. Particularly in early generations, large stature was the norm and even the Anunnaki hybrids towered over the indigenous people of that era.
Here again is a sad saga of domination and subjugation of human beings living in those times who were commandeered to serve the Anunnaki, and their hybrids as reigning deities, but truly interlopers with no right to intrude. They enslaved the humans and subjected them to much barbarity. This led to a rebellion that was done out of sheer desperation but without a realistic chance of successfully displacing the unwanted rulers. As punishment, the extraterrestrials committed an act of genocide and decimated this human colony, and what you see there is the remnant of their handiwork. They did it in stages to make the survivors bury the dead while knowing, eventually, they would get their turn. This is a perfect mirroring of the depravity of the Nazi death camps doing the same to political prisoners, Jews, and others out of favor with the Nazis—the inmates themselves did much of the dirty work, dealing with corpses, and so on. So far from being a relic of a peaceful time of happy coexistence with benevolent extraterrestrials visiting the planet and sharing good times with the humans of the era, it is the exact opposite, to the most extreme degree one could imagine, in terms of their ending up not only subjugated but decimated by the interlopers.