So a haunted house is different to a monster just because?
Been out of the thread for a bit, and you weren't talking to me. But my answer would be, "A haunted house is a location, and locations don't move, while creatures generally do." Now, I might invent a haunted house and
place it in an area I expect the players to visit, but I see that as very different--that's populating a location before the players arrive. Yes, populating a location
means me as DM inventing fiction to fill what was an empty unknown. I'm just dramatically less comfortable with "this location simply appears wherever the players decided to go" than I am with "once the players
have decided to go somewhere, it needs to be a Something and not a Nothing." (Reading your most recent post, I'm deeply uncomfortable with palette shifting, but not with painting the background as I need it, so to speak.)
Do you use a different random encounter table every time the players make a choice of direction?
Only if the choice of direction is enough to
be a difference. That is, if the party is still riding around in the Skull Woods, they can expect bandits, weird land anemones, spiders, animated skulls, flying jellyfish, etc. Choosing to go to the left
while staying within Skull Woods is not,
in this sense, different from choosing to go right. That does not mean that choosing to go right vs. choosing to go left has ZERO differences whatsoever, it just means that that choice is not one which applies to changing the random encounter table.
If, however, the fork in the road would send them to Skull Woods if they go left and Mt. Gulg if they go right,
then that choice absolutely would (and should) change the random encounter table, because that IS a choice which applies to the things one would expect to find there. The dark and spooky forest should differ from the depths of caverns, if only because the food sources are quite different.
Because if you don't the players choices of direction are meaningless in regard to what they encounter.
See above. Some choices rationally should not have impact in certain senses, depending on context. That does not mean
absolute invalidation of choice.
The problem with the teleporting haunted house (unless, I should note, it actually IS teleporting--which is perfectly fine if you establish it and empower the players to learn about it, whether or not they actually do so) is that it invalidates a choice that, rationally,
should matter for this subject. A physical building
should be accessed only down one path, unless time and effort cause you to come back around to having chosen the other. Presenting the choice of path to take necessarily implies a
different destination, unless and until you justify that the choice shouldn't. (E.g., some roads that fork may only be going around an obstacle, and thus meet back up again once past the obstacle.) Presenting the choice of which path to walk
while staying in Skull Woods does not necessarily imply a different ecology, in fact, it is generally understood to imply the opposite, that the ecology should stay the same.
And yes, this does make things at least a little bit subject to interpretation--as it should be. I don't believe there is, or should be, some utterly mechanical procedure for avoiding railroading, because that would be trying to solve the problem of being too formulaic
with another formula. It has to be a judgment call, and it is quite possible for the DM to make a bad call. That's part of learning. But the overall heuristic remains effective and, barring the occasional exception, it
is an effective pattern for avoiding railroading, particularly its worst excesses.