This line begs to be modeled. I think the power unit from the Bachmann trolley car would make a good start for the locomotive.
https://www.youtube.com/watch?v=P17Wo7ytxlc (https://www.youtube.com/watch?v=P17Wo7ytxlc)
Neat little cars there. I've never seen self-driving train cars before. Maybe there's just some second loco I'm missing.
I think if you look closely you will see that the cars were left on a "hump" in the track. They had a brake or something stopping them from rolling until the engine was on the siding . Then they were released and off they went down the track and passed the engine. It is easier to see the high place in the track when the train is leaving.
Tom