I would add to that...that no one KNEW wtf was happening at that second.
The guys were approaching the siding, on signals. The signal dropped. Procedure is to bring the train to a safe stop - not to dynamite the brakes - and watch for other abnormal issues that may have caused the signal to drop.
They may or may not have realized right away that the train approaching had run the signal. They would have been hard-pressed to figure whether that train would be able to stop short of the foul point...and if it had? And the crew on the camera-train had big-holed the brakes? And the train broke or tore out the turnout with the sudden braking forces?
At some point they clearly DID see that the train was going to run into them. The instinct is to put the train in Emergency. ONCE THAT IS DONE, THE BRAKES CANNOT BE RECOVERED FOR 5-10 MINUTES.
Had the crew sped up, the head-end may or may not have missed contact. The opposing train WOULD have hit, and his consist may have come off the rails...piling onto the train entering the siding. The more speed on EITHER train, the more violent the collision. (Forces multiply by a factor of 4.)
It could possibly have been (in the engineer's split-second appraisal of the situation) that he was mistaken. That train may just have been crowding the signal...and there could have been a standing or rolling car on the siding. And if he hits? And someone gets killed? He's liable...for accelerating, not braking, when his signal dropped.
Railroad operations, and dealing with emergency situations, is complicated, friend.