Good Explanation!
Since a derail was used, it was likely protection for Roadway Workers on an "uncontrolled track" (authority from dispatcher not needed) or "other than main track", where all movements are required to stop short of,........which includes derails.
In any case, as with all railroad accidents, this is all speculation without any of the facts available.
For those who want to further understand the intent of Roadway Worker Protection (or need something to help you get to sleep), see
49 CFR Part 214.
More information on incidents can be found at
FAMES.
MDR