I know a lot about this train and have posted forums about this particular train before.
The train was loading at the Railton Cement loading facility off to the main line with the remote with the driver who would've been standing in the Railton silos and once he would've finished loading two wagons he would've released the brakes and powered the train up so it would start moving and then normally put the brakes on and cut the throttle off and line the train up to the correct positioning for loading the next two wagons. Obviously whilst the driver has been trying to do this something has gone wrong with the remote once he's started applying the throttle to move the train up. The remote system doesn't have a very far range and I believe it's not much further then what the length of the train is, so in essence once the train has kept going there's nothing the driver would've been able to do but to watch the train just keep moving until it became out of sight.
The remote mustn't have any type of vigilance system on it which the TR locomotive is fitted with but must be disabled when the train is being controlled via the remote. The marker lights on the front of the TR become red when the unit is being controlled by another unit or the remote.
Watch these videos and you'll be able to get a glimpse of what I assume has happened but then again I can't confirm this.
https://youtu.be/8mai0oqLkg4
You can see the remote control action here loading the train and unloading the train.
https://youtu.be/irzSX4MbITo
This shows the remote set up unloading at Devonport, notice the red marker lights and when they load/unload they usually drag the brakes to help line the train up correctly.
https://youtu.be/VHU4YmLyFaQ
This video shows that even if the points are set incorrectly at Railton the train pushes them over so even if the points at Railton were set incorrectly the train would've just pushed them over.
I hope this helps explain the situation!