Read the NTSB prelim report, it describes a lot of details you appear to be struggling with.
The train struck the left rear of the truck which damaged the left front of the locomotive.
It states the forward facing train camera shows both crossing arms were down.
It also states there were two locomotives on the train and it's clear from the photos it was push/pull, not double-heading.
I think the sudden and violent counterclockwise rotational thrust of the truck body killed the far right truck passenger as the cab would have literally smashed into him even though the cab was not struck directly.
Could/would you please share the URL with us?