I discovered this while just messing around trying to find another way to pass through the train. As it turns out, there is one. By holding down the down arrow key and opening a new tab without releasing it, and then waiting a couple of seconds before switching back to the game, your character will walk through the train.
Unlike the previous method, which was very incosistent and hard to pull off, this one is super consistent and will work pretty much 100% of the time as long as you're doing it correctly.
Sadly, I don't know how this would work for a downloadable version of the game. I haven't tested it myself, but maybe there's some alternate strategy? I don't know.
Video:
I think this would definitely be categorised as a glitch so i really doubt its allowed in any% glitchless
I haven't tested it on flashpoint, so I don't know why it doesn't work on there, but it seems that this trick also works with opening any other application, not just a new tab. If you do it that way however, both drakens värld and the other application need to be in fullscreen, otherwise it doesn't work.
Also, about the music thing, it seems that having the music off causes the game to freeze after a short while until you switch back to the game, and so you can't walk as far as you want. But from what I tested, it seems that you can still manage to just barely get past the train if you enter the screen with the train first and trigger the glitch right afterwards.