head injuries are the last priority when providing first aid, the first two are security (get him off the train) and massive hemorrhage which is exactly what the medics did, they weren't exactly gentle when they yoinked him off the roof. this is cause one can survive as a vegetable caused by aggravating a head injury, but can never survive if they bleed out or lose circulation.
i managed to find both kids' tiktoks before the survivor wiped them but don't wanna dox them, it looks like they're actually experienced in urbex/train surfing and just had a bad accident.