Did the ump make an out sign with his arm? That's what he seemed to do. That is what the fielders saw and walked off the field. Verbal decisions are needed so everyone can hear - enough of the umpire motion performance horsesh't.
The umpire said that he goes by the expressions or movements of the batter, if you can believe that. I mean, how could he even tell from where he stands if the ball was caught or not?