I am not surprised at all that the bird would learn to hit a drey. These birds are rewarded for learning, whether they are working with a falconer or on their own hook. The act of hunting prey involves problem solving, recognition of patterns, and using deductive reasoning to make those wild leaps of logic.
And the squirrel is constantly learning new methods of escape, too.
In both cases, winners get to breed, ensuring offspring are faster, smarter, better, stronger, etc.