CA Screamin's programing has been changed to prevent the ride-ops from doing a manual reset (by switching to maintenance mode) since cast previews in 2000/2001 when a similar accident almost occurred. A friend of mine who used to be a lead on Screamin' prevented the previous accident and said that the reason it almost happened was when they switched over to maintenance mode, the sensors lost the train sitting in the same block section the train was sitting in this time. Luckily, someone noticed and e-stopped the ride before the train hit the block before the helix.
Based on his knowledge of the ride system, he believes there is no way operator error was the cause. And based on the speed of the train (resulting in the "bump") The block brake before the helix would have had to completely stopped the train as it passed through it, and then released it. Otherwise, there would be a lot more damage.