High speed for that set up would be about 80mph max, and definitely not that fast through that stretch of track. Definitely some speed restrictions going through there. So it could be operator error, not following speed restrictions, equipment malfunction, track problem, collision, or sabotage.
We won’t know until the investigators interview the engineer, and review the event recorder data and video downloads.
Lived in Vancouver, WA for years and have taken this train many times to Mariner baseball games. This is sad, especially this time of the year.