But this is impossible as one part of the device sits on the track and the other part of the device is on the underside of the train - and there are many of them so even if one is disabled the others still work. The driver does not have access to this system.

Yes there are big potential risks on the railway, but this may not have been one of them. It's unlikely that the driver can do anything that will lead to an actual collision as far as I know. But again - I do not know the facts around this particular case, so, unlie others, will not jump to any conclusions.