True but this only applies up to the posted speed limit. You are never under any circumstances allowed to exceed the posted limit per 22348: codes.findlaw.com/ca/…/veh-sect-22348/
What you posted means you are not allowed to drive faster than is safe for the road conditions. 65mph in a 65 is too fast if there is dense fog for example.
“Its OK to speed if everyone else is doing it” is not part of any law or in any handbook.