Actually it is in San Mateo county. Wikipedia: "the airport is owned and operated by the City and County of San Francisco, despite it being located in San Mateo County."
It is a little confusing for me that the city owns or administrates a number of sites outside of what we think of as "San Francisco". It's not been clear to me if you "re-enter San Francisco" when you go to those places. I figured yes. A number of them have signs posted at entry that the city owns it, so it feels like a natural conclusion to make, as if a "now entering..." sign.
That's not what "technically" means. From the Wikipedia quote, it's literally not in the City and County of SF and is just owned by the government. It's very much south of the city because it's technically not in the city.
It is a little confusing for me that the city owns or administrates a number of sites outside of what we think of as "San Francisco". It's not been clear to me if you "re-enter San Francisco" when you go to those places. I figured yes. A number of them have signs posted at entry that the city owns it, so it feels like a natural conclusion to make, as if a "now entering..." sign.