A lot of the stone they worked was/is limestone or calcareous rocks like dolomite. I saw a documentary where their masonry technique was demonstrated: They wet the rock to soften it and used used copper tools and water as cutting fluid.
For granite, they probably used two granite pieces: one granite block to sand and polish the other. You can create very flat and straight surfaces this way.
I think I saw that documentary.
It’s very arrogant of us to think that ancient people were not clever & resourceful. The default doesn’t have to be aliens!
That way works to roughly cut stone but not to carve complex designs in any way accurate to millimeters.