That’s some airtight casket - check out the last shot in the embedded video in the article. In the 19th century the city closed all the cemeteries in the city limits and relocated the bodies to cemeteries in Colma and elsewhere for space reasons. Obviously they missed one.
More than one. They show up from time to time. Not all bodies got moved, after the order to vacate cemeteries from SF. Sometimes only the tombstones were moved. I think some bodies showed up during construction of a library and museum in Civic Center recently, as the parcel between City Hall and Market Street used to be a cemetery in the 1800s.
Here is a good article on the subject of SF cemeteries moving to Colma. One of the historians contributing to the article, is a history teacher of mine from over 45 years ago, now a historian famous for California history (Michael Svanevik). Mentions the many hundreds of bodies left behind. During construction of buildings, they sometimes put piping right through bodies found in the earth.
I had a great SF history teacher when I went to CSM, I think his name is spelled Svanevik. Flaming homo but a good guy, never put his hand down my pants.
He said flat out that many dead bodies weren't "missed" per se but were left ON PURPOSE by unscrupulous companies contracted to move the bodies.