Most likely Sheila spoke to the ambulance service first; the operator must then have decided to connect the call to the police.
Once the call is connected the operator is disconnected. Why would he/she still be on the call? Plus we have the operators statement, which completely contradicts what Milbank is saying now. Also, you say he was told to keep his mouth shut, but he says he wasn't asked about it until now. Like I said, it makes no sense!