Well, speaking as one who rides commuter trains on a regular basis, you should know that there are lights on the track that indicate to a train whether or not it is safe to proceed. If a train ahead is stuck on the track, for example, the light turns red so that trains behind can stop.
There is usually more than a visual indication. Typically there are failsafes
Something went terribly wrong.
Yeah, if the UP train had run a red light at the top of the hill, the Metrolink would have a red leaving Chatsworth station wb.
If the UP had a green light at the top of the hill, the Metrolink would have a red light leaving Chatsworth.
Either way, the freight train was in the block ahead before the Metrolink passed their last signal....and the switch was lined for the freight to take a siding (which Metrolink had passed)