Odd. I thought the report was that he was on the medical call and left it when he heard the radio call about the robbery.
Transcript is not clear but it seems like the officer had to have heard the call on the radio.
"So I just want to give you a little time line of what happened on August 9th. From 11:48 to noon, the officer involved in the shooting was on a sick call in Glen Arc. There was an ambulance present. At 11:51 there was a 911 call from a convenience store nearby, not this one. At 11:52 dispatch gave a description of robbery suspect over the radio. A different officer arrived at the store, where the strong-arm robbery occurred. A further description, more detail, was given over the radio and stated the officer was walking toward (sic), or the suspect was walking toward QuikTrip. Our officer left the sick call, he encountered the, I'm sorry. At 12:01 p.m., our officer encountered Michael Brown on Canfield"