From what I watched, and based on my non-expert opinion:
He was loose. Game plan or not, he saw what was and wasn't there, and made the throws he was supposed to make. And the ball came out quickly.
That Raiders defense was either bad or not prepared. Probably both.
The guy has some swagger to him. He did his job for Sunday. He was prepared and knew what he was supposed to do. And he executed. Can't take that away from him, no matter how much you love Fields.
Ceiling is probably Heinicke. Which isn't bad at all.