He probably knew that there around a bunch of hospitals around the geographic center of SF (if you live in that part of town it’s hard to miss), and then did a Google search for the numbers. I used to work at UCSF and this matches my sense that there are a lot of medical facilities in town.

Yeah I know where the hospitals are in San Francisco because I lived there. Centrally located isn't as great as it may seem. For the others I just plugged "emergency room" into Apple maps and picked some points that seemed close enough together.