When people outside of LA say "Los Angeles", they're almost always referring to the county. The city of LA is actually quite small.
For "San Diego", it's precisely the opposite - a giant portion of San Diego County is comprised of the city of San Diego, and they're almost always just referring to the city.
And for "San Francisco," the city and the county are basically the same entity and thus have the same borders.
When people outside of LA say "Los Angeles", they're almost always referring to the county. The city of LA is actually quite small.
For "San Diego", it's precisely the opposite - a giant portion of San Diego County is comprised of the city of San Diego, and they're almost always just referring to the city.
And for "San Francisco," the city and the county are basically the same entity and thus have the same borders.