Everybody knows it's safer to live in the country, but that's not the argument he's making. He's saying it's also safer to live in any other city. I don't know if it's a great methodology though, going per sq mile.
Some counties have a single ambulance, and are 1-2 hours from a hospital.
Where I live, there's only volunteer fire departments. That can't be great either.
People just love hating on SF and/or cities in general, and will dig up any statistic that supports their viewpoint.