[TXnMA]

Good observation! The front photo was taken by a Congresscritter, so we know that was their front unit. Look at this aerial photo from the article you linked:

The rear "pusher" engine unit was from another "consist", so it was in different "livery". Both, of course, were Amtrak units...

[Steven W.]

As I recall, that day, there were reports that after the collision at the crossing there was another incident right thereafter when another truck struck the rear of the train. I'm still trying to reconcile the photos & the witness statements, both at the time and in today's report.

[Swordmaker]

The rear "pusher" engine unit was from another "consist", so it was in different "livery". Both, of course, were Amtrak units...

From the debris pattern, and the damage to the original engine, the train was traveling from our right to left in the above photo. Recall there was a curve as the train approached the crossing, and we can see there is no curve where the train is no sitting, so that is the exit from the approach. That’s the only way the the debris can be explained to be strewn from the crossing at the extreme right. The "pusher" engine was brought in to move the train from the rear, whether as a pusher or to pull it back the way it came.