Train Spotters (fans) chime in!

So, I’m walking home tonight through Encinitas and I see the northbound Coaster(commuter) train heading north about 100 yards ahead of the northbound Surfliner (Amtrak). How did they ever get so close?

My job and hobby let me know a fair amount about trains and signalling and such, but I couldn’t think of a scenario wherein a train can creep up on another train headed in the same direction. There should have been an “absolute stop” somewhere behind the Coaster, shouldn’t there have been?

Like I say, I know a fair amount about trains (and even drove one once) but this sight just has me flummoxed…

This site mentions trains on the same track in its first paragraph and goes on to state that safety is first and that there are signals between the two trains that absolutely allow for the following train to stop in time.

On the LIRR and NYC subways - trains use the same tracks all the time (of course) yet typically the following train will hold short of a station platform by hundreds of yards.