It actually would have been easier I think to derail the train. Just pick a section of track on a curve and remove the stakes/bolts from the outer rail. (probably even more effective if the train is on a downhill grade during the curve). Depending upon the track you may have to unbolt the fishplates too.
I agree. Which is what I was suggesting by saying they didnt need an explosive device but they would certainly need tools and manpower to go that route. I dont know much about trains though.
When I was in the military my MOS (Military Occupational Specialty) was initially 12B Combat Engineer. This was basically construction and demolition of roads and bridges as well as landmine warfare. Construction mostly consisted of prefabricated constructs that needed assembly. Demolition involves explosive devices like a Bangalore torpedo, C4, blasting caps, det-cord, fuses and so on.
So naturally my first inclination would be to blow $#!% up. Its easy and fast not to mention they had access to what they needed. The train was presumably protected but the rails werent so you go with the easiest target in the allotted time you have. Disassembling the railing works but its much harder work and time consuming.
Also, for what its worth, when they were on the train they presumably could have just disconnected the engine from the trailing cars. Leaving them stranded possibly without horses.