Corrections: Not 911 operator, dispatcher...and he never indicated to the dispatcher that he was returning to his truck. That part is supposedly in his statement to police after the shooting.
He called 911 where there was a 911 operator which is different from a police dispatcher. Again, the Sanford PD (in their own statement to the public) said the 911 operator did not command Zimmerman but only suggested he not follow Zimmerman.
I heard right on the audio that he said he was returning to his truck after Trayvon fled into the darkness. He then concluded his call with 911. You might go back and listen to Zimmerman’s call again if you even did it the first time.