Correct me if I'm wrong, but it wasn't a 911 call.
Mr. Zimmerman was talking to the police DISPATCHER.
You're correct. George Zimmerman called the non-emergency number for the Sanford police, not 911. The City of Sanford made that clear in its FAQ letter, and the State of Florida makes that clear in the charging affidavit for the second-degree murder charges.
The media hasn't caught on to that yet. or don't want to catch on.