I think that system was dumb. When to call for a challenge should be when you think it's wrong. If you keep using up challenges because you have a bad eye, then you get a red light. They have unlimited challenges if correct.
It's how he holds it. I think his index finger is gripping it as it would in a knuckle? It means that finger doesn't contribute (or hinder) the spin he wants to apply.
I guess he did have an element of surprise and the infield was back. But it also shows how little faith he had in himself of getting a hit by swinging.