California has a homeowner-occupied tax exemption, and it is listed on the county assessor's website whether a given property is taking it (at least it is for a

California has a homeowner-occupied tax exemption, and it is listed on the county assessor's website whether a given property is taking it (at least it is for a relative's property in CA I just checked). So I expect they're using that. This might undercount (if owners don't file the form) or overcount (tax fraud or error), but there's financial incentives to get it right on both sides, so it's probably fairly accurate.