"When in Rome" is the first half of an old adage: "When in Rome, do as the Romans do." It means that when you're in an unfamiliar location, take your cues on what to do from the people who live there. It doesn't mean that they're literally in Rome.

It's being used somewhat incorrectly in this title; to say that the Uber driver is just doing what's normal for Bay Area people, I guess.