You are correct this is the intent of the rule is to stop the cat and mouse between pitcher and runner. But you say in this case it was not happening. I don't know I can't read the runner's mind. The runner was standing there, Cat was not having anything to do with it turned and walked into the circle. The runner was returning to the base but not until standing still for two second after the ball was inside the circle.

The rule book states the runner must move immediately, This puts the judgment on the umpire. I feel two seconds is time enough to find the ball and start moving back or forward to a base. Your judgment may be three seconds, or maybe five or maybe stand there until you decided the runner is playing cat and mouse. If that is your judgment that is fine. I just don't call it that way.