"How exactly could nomadic people develop advanced masonry skills?" By being half nomadic. When you move around and set up camp often and build temporary struc

"How exactly could nomadic people develop advanced masonry skills?" By being half nomadic. When you move around and set up camp often and build temporary structures out of wood, there is opportunity to learn masonry. And when you often visit the same places, and evertime you add something permanent and more lasting, then specialists will develope. Nomadic people were usually not changing place everyday. They changed places, once the game in the area were exhausted or the temperature became too cold/warm. But next year, they come back to a good spot. And so over the years important spots can get sophisticated buildings.