Lol, someone got a policy violation...
Avalanche's Reptilian's board is still pretty much a manual affair. While trains will advance the blocks automatically, there are certain functions that are still the responsibility of the Board Operator, like moving trains into and out of the station. This is one of those situations.
What most likely happened was the Board Operator was not paying attention to the train as it entered block 4. When trains are running slow, there is a manual set of drive tires they can use as the train enters block 4 to give the train a boost. It only works though if the train is still moving as it enters the block, because it's not strong enough to pull the train from a dead stop.
The other thing that could have happened was the train lost a wheel, which does happen on occasion.
Either way, it's not really that abnormal.