at the end of that train car in the picture, you can see the rolled up roof of the train. this is after the train passed under the bridge, so it must have been sucked down under the bridge and scrapped the top of the cars
even in the video, there’s not nearly enough material at the edge of the bridge to account for multiple train cars worth of roofing. it’s just collecting a certain amount and the rest is passing, probably rolled upside down and under.
i wouldn’t have been brave enough to stand up on that bridge to film. idve expected some bits of metal exploding off with the force, or a weak bridge to collapse.