Thanks for reviving this thread and for the further thoughts, most of which I agree with. But how do you bring in Warrington? The journey commemorated in the song was NW out of the Manchester area, going at least as far as Hebden Bridge.

I agree that "reload" doesn't make a lot of sense. Maybe they were supposed to drop some wagons off there and/or collect some. A derailment could have occurred in the course of shunting into or out of a siding.