Lower left of the bottom photo shows the first stage landing deceleration burn as it heads back to the launch site. This was the first return-to-launch-site (RTLS) for SpaceX launches at Vandenburg AFB, and the first RTLS for a Block 5 booster (all the rest were droneship landings)
Man, that's gorgeous. In many ways: Great photo. Great plume. Great technology. Great to see America doing something positive and inspiring, rather than just beating up brown people all over the planet.
am_Unition is spot-on. Vandenberg launches typically are for sun-synchronous polar orbits, so they launch south/southeast along the coast but over the ocean.
There's tons of 'range safety' work that goes on with these launches. There's an envelope that the rocket is approved to fly within on its way from the ground to space. Most flight termination systems are controlled by hand--a radio signal can be sent by mission control to remote-explode the rocket if it's deemed that its a risk to something on the ground. SpaceX is unique at the moment (as far as I know) in having an automated termination system that passes control of that termination decision to the rocket. You can read more here.
(as an aside, this photo was taken 300+ miles away from the launch site!)
Vandenburg is for polar orbiting satellites, so launches are always oriented southwards, which is out over the ocean. So yes, at no point is the launch passing over any people, save maybe a few cargo ships every now and then.