Its not that far from the road up to the rail bridge - sufficient explosive power and maybe some fuel with it would do and obviously did create a large enough fire ball to ignite the fuel cars.
So, you’re sitting at your laptop, controlling a submersible drone, watching the cameras trying to decide when to launch your whatever it is.
Can you time your launch so as to coincide with the passage of a train? Probably.
Can you time it so as to coincide with the passage of a tanker car carrying something flammable? As opposed to a flatbed, a boxcar, or a tanker carrying something that isn’t flammable?
Unlikely.
And here’s another thing. If the explosion set the train alight, why are the cars immediately opposite the explosion?
If the train was moving when it caught fire, you’d expect it to have moved half-a-mile or more before it could be stopped.
Was the train stationary at the time of the explosion?
The more I look at this, the less certain I am of what happened.