Guerrilla urbanism is pretty much illegal to do everywhere, including in the article's subject city of San Francisco. The goal is to not get caught by authorities while doing it
As for the guerilla bike lane on JFK Drive in Golden Gate Park, that entire 1-mile section of JFK was later closed off to cars entirely. It required a city-wide ballot initiative, IIRC, and was very contentious. But the city government was in favor of it, which may have something to do with why they were so accommodating earlier with the bike lane.
It's still very contentious and was on the ballot again yesterday to undo the previous ballot measure and make it available to car again. The proposal to undo was defeated.
I present… [https://en.wikipedia.org/wiki/Ken_McElroy]
Nice slippery slope, btw.
I bet Romania has something similar.