My guess is that Rauch was simply pulled because he got into trouble and the leash was short. They had to sweep to make the playoffs, so the manager isn't going to be real patient with a guy if he gets into trouble. He'll yank him quicker than normal.
KW did say that they wouldn't promote anyone until after Charlotte was out of playoff contention, so I doubt he was pulled due to promotion. If that would have happened, he either wouldn't have started the game or he would have been pulled after an inning and not during one.
Just a guess....
A guess