Yes there was. And it was malfunctioning. Since at least the day before, as some train engineers reported. So they were doing it old style in the meantime.

Signalling, especially in another country, is not my specialty... But stateside (where tech can range from 2026 latest to akin to 1926).. there would have been a trackside signal that the moving train would've had to ignore... On top of the dispatch/comms screw up. I, like you, would have assumed there'd be some positive control preventing the trains from being on the same section of track or at least at high speed. Hopefully this will spark safety initiatives to improve signalling and train control.

They were supposed to move the same way. There was an issue with the signaling somehow so they had red lights, but the traffic controller overrode it by telling them to go. Had both trains started moving instead of just the back one this wouldn't have happened.