Legitimate question: what is the difference between doing this beforehand vs in the moment?
A DM that does it beforehand is similar to a DM that does dungeon ecology beforehand. Remember when the dungeon had skeletons in one room, a shambling mound in the next, a couple carrion crawlers in the hall, twelve bugbears sleeping next to a black pudding, and then a vampire? That was because people were just interested in one thing, the fight and treasure. Then along came someone who asked, why is that vampire in there? (Poof, Ravenloft, the story adventure, was born.) They started thinking about dungeon ecology, and suddenly, the adventures started making more sense from a story standpoint.
Remember when a map had rivers that just ended, or falls that could be heard twenty miles away, or deserts in the middle of continents with giant tropical jungles in the middle of all that sand? That was because people were just interested in a setting for exploration and combat. Then along came someone who really thought about topography, what was common, what was uncommon, and what doesn't exist. Those same people started making more realistic maps, and suddenly, the world started making more sense.
I say all this because those are two examples of doing things beforehand versus in the moment. Putting careful consideration into those things literally changed the game.
The same is true for coming up with paths beforehand. They can be created by the DM alone, or by the DM using player input from the last couple sessions or character backgrounds, or in some table's cases, by just the players. Coming up with those things ahead of time allows the DM to anchor the party's objective. And in this case, it was to escape the Feywild. It allows the DM to compare/contrast the party's chances. It allows the DM to have a backup plan when the table decides they don't know what to do. And most importantly, it keeps the DM honest. It also has other boons to certain players, but that is beside the point.
And again, you can have a different definition. That is ok. I respect your opinion and your ideas behind railroading. I tend to agree with a lot of what you say. I just happen to add an extra page. And that page details why coming up with things in the moment can be just as much railroading as the DM who wrote down one path, one solution, and is forcing the players down the path and onto the solution, which is probably already predetermined.