The population of San Francisco proper is only ~800k but the population of the Bay Area as a whole is about 7 million people, which is only slightly less than Greater London's 8 million.
Why is this relevant? The Bay area is not San Francisco. The post is comparing London with San Francisco. San Francisco is tiny compared to London in both area and population.
San Francisco the political entity what is that? At any rate the blog post isn't about politics at all.
San Francisco is a city and the "Bay Area" is a region. In London people from both Chiswick and Hackney which are quite far away from each other both say they are from London. Someone from Sonoma and someone from Santa Clara don't say they're from San Francisco.