It seems plausible that SF already had such low inventory numbers that any change would look huge on a chart like this, though that doesn’t appear to be the case in the other highly competitive markets seen here. I’d love to see the actual monthly figures... maybe it’s true that there’s an exodus afoot, or maybe SF was that much worse off from an inventory perspective until now.
It also seems plausible that SF has a unique combination of factors that put it in a bad spot right now. It’s insanely expensive, quality of life has been on the decline for some time, and the types of companies that made real estate there so expensive in the first place are also likely to be the ones that adopt remote work quickly and wholeheartedly.
SF aside, my best guess at this point is that many American cities are and will continue to actually see some amount of people leaving for lower cost and more spacious markets, especially if remote work optionality sticks in the way it looks like it will. But cities have enduring appeal - proximity to people and culture and things to do is just as much a factor as proximity to work. I think any exodus we see in most markets will amount mostly to a pull-forward of people who would have left cities anyway because of life stage, but did it a year or two early if they could.