By 'shunts" I assume you mean shorting the signals, to stop the trains?
If they're willing to do that, I wouldn't put actively trying to derail one beyond them, but the stories I read said the derailment was at or near the rear of the train, so I suspect that it wasn't tampering.
They had a winter storm go through Monday, with some dramatic temperature swings, and heavy rain, so it could be a track issue related to that. But that's just my uninformed speculation, from 2500 miles away.
It's interesting that this apparently didn't make the national news. A few years ago every media outlet would have it as one of the top stories. Maybe because it's in the Northwest, which news services don't usually talk much about?