 Why is the Sand God causing a terrible storm?
A gray, funnel-shaped cloud of dust stood off to his left. Weather control made cyclones and other climatic phenomena on earth practically non-existent. He examined the wind devil as closely as he dared, but it was composed only of grains of sand. But then, how could a group of loosely spaced grains of sand possibly have a nervous system? He became so absorbed in doing this that he failed to notice how the wind devil drew closer and closer, but when he inhaled the first grains of sand, the realization of what was happening dawned with a flash of fear. "As for the webfoots," the wind devil, or Sand God, said, "I will destroy them. The Sand God did not reply.
 He is angry because he doesn't understand Stinson.
 He knows he can't control Stinson.  He is angry because Stinson figured out he is a child.  He is angry Stinson took Sybtl away from the webfoots.  He is angry because he doesn't understand Stinson.