[JCMcAdams84]

I've been called to enough car accidents in my time to know that the human body moves in weird ways when it is the victim of trauma and force. Hitting the window and then slouching back into his seat isn't only possible it's likely. The windows on a train are often double or triple thick or even plexiglass, which to break would need a lot of force. If the train's rear car's derailed and pulled his cab to a stop he would fly forward at the speed the train was going before it stopped because he wasn't wearing a belt (since most trains don't have those in the cab), upwards of 40-50 mph. Hitting the window with the force to crack it but not fly trough it like he would a car window so his body would fall back, likely into the seat and the whiplash would put him into a somewhat seated position.