The "facts" I've seen reported:
* The tracks were recently upgraded to handle higher speed rail traffic;
* This was the inaugural run using that newly upgraded route;
* The tracks were rated for 79 mph;
* The train was going 81 mph;
* There may have been an object on the tracks.
"Facts" in early "news" reports are subject to update and change, but based on what is known, the cause was either excessive speed (I kind of doubt this, since ratings are often conservative), defective workmanship affecting the actual maximum speed, or an obstruction. There is speculation "out there" that Antifoids sabotaged the tracks with an obstruction, but much as I loath them, proof is lacking, currently.
Right now, unless DU-moron "Ken Burch" is privy to knowledge no one else knows, he's pulling factoids from his rectum, and at least some DU-folk are lapping it up.