From that 1 video it is set dead center on the big trailer. I've no clue what you can see differently??
I see it slightly above. That's not what I am thinking of though. That might be a misinterpretation of the video on my part. Explosion analysis is not my forte.
If there are more blasts then these could be other stuff such as planted explosives or unmanned subs etc. But video itself is showing a single detonation.
That's just it. There are three spans fallen. Two are together and next to the burning portion of the train, where I would expect from the truck bomb. There is another span ahead of the train. That's probably not caused by a truck bomb.
If there were multiple vectors of attack, the makes it less likely to be a truck bomb to me. A truck bomb and some other way is overly complicated and far more likely to be caught and/or fail.