I noticed that the inner wall surface and the wall of the column are processed equally, for what
and why? That is, in other words that supposedly with picks digging - it's just nonsense, clearly visible mechanical processing, as if bored, or rotational movements of cutting tool . Version with cutter is most likely because the blocks themselves have the cone form.
One must try to answer the question of "how", in a personal way. A site like this is difficult to excuse as just crafty ancients with simple tools. I tend to think there is some lost technology, advanced or not, that was employed here and many other enigmatic sites around the world.