what if when Tony snapped his figures..

I think the stones are sentient to a degree... meaning they can sense things. They have an intelligence of their own, and since the mind stone is one of them, I believe it gives the wearer a certain telepathic ability tied to the stones. It can read what the wearer wants to happen when he snaps his finger. Thanos wanted to wipe out half the universe in Infinity War, and if Tony had not gotten the stones away from him, he would have reformed the entire universe to his will.
Tony was probably thinking "Turn Thanos and his army into dust!"