Judging from what I've seen of SF politics its much more homeowners, who have far more power, than landlords.

A landlord is, by definition, a homeowner.

i think they are completely separate?

landlord: may or may not own a home, but have a property to rent out, may it be a residential or commercial like a warehouse. They may not even own the home they live in, which is surprisingly very typical to cut cost and deploy money in other ways.

homeowner: own the property they reside in.

In this case the commenter is specifically referring to the class of people who own a home they live in.

owner-occupier is the usual term