The only way I could think of something like this happening is that the train in the station was either advancing into the station and getting ready to unload or loaded and ready to dispatch, and the train behind it kept moving due to an error in the computer system. The drive tires only function to advance the train in or back the train into transfer, if a train is already in the station it should've stopped.
In the picture the combs (floors) are not fully up, which lends credence to the idea that the train that was in the station was either unloading or ready to dispatch. If the trains collided it was probably at simple advancement speed which was only a few mph. This is based on the guests riding the train that collided saying they were originally stopped. The only way this sort of incident could've happened was a programming oversight and the right conditions were satisfied in order for it to happen. I have not heard good things about Valravn's programming from anyone who was involved with the ride its inaugural season and Cedar Point has a noted history of slightly modifying their rides in order to try and increase capacity, so I figure this incident was a matter of time coming.
Train collisions happen more commonly than you may think, they usually happen when guests are not present during safety checks. There's a reason why most trains come with padded bumpers, the manufacturers and parks know this.
TL;DR - Serious, but not major incident happened that likely was the fault of perfect conditions and possibly a programming oversight.
PSS - When Cedar Fair rumors ramp up for 2020 and beyond I'll elaborate a little further on what this means for Cedar Fair and B&M.