The stones in question are sandstone, and look like sandstone. It would be wishful thinking indeed to see them as granite. The workmanship is indeed superb and precise, showing great craftsmanship, expertise, and geometrical savvy. They apparently prefabricated many of these stones at the quarry in precisely produced shapes that were interchangeable, very clever indeed. The craftsmen who worked these stones were in possession of metal tools, as should be obvious since one of the most interesting aspects of this stone work is the metal butterfly joints they used to hold them together. There is no question that these people were very very skilful, imaginative and inventive.
The idea that because you don't know how to do it, it must be the work of nonhumans is nonsensical, egotistical, ethnocentric prattle. Those folks were great masters of their art, but they did not need gods and spacemen to teach them how to carve rock, or some dude on the internet to tell they couldn't. The credit is all theirs.
