There are a handful of airports in the US, SFO among them, that were/are part of a program that used private security contractors that operated according to TSA SOP. If I remember right this was just a pilot program that was discontinued, but the existing airports were grandfathered in.

That said, I haven't been treated any better by Covenant Security's (the contractor for SFO, aka "TEAM SFO" as you see on their shirts) people than I have been by actual TSA employees elsewhere. Seems like a nominal difference to me.