Let's take another quick look at the Goblin Guard Room enounter, the map of which appears above. It's an example of a kind of equivocation.
A DM is typically caught in the fork of two competing objectives. He wants to provide players with a range of options, to make them feel like they are expressing themselves by way of decisions with meaningful consequecnes. At the same time, he wants to structure encounters in a logical progression, so as to provide players with a coherent story, a well-paced play session, and a rewarding difficulty curve.
One solution is equivocation.
This is a term that comes from stage magic, where the magician presents a false choice. For example, the magician may offer someone the choice of two cards. The magician wants the person to end up with the right-hand card. If they select the right-hand card, the magician says, "An interesting choice! Take the card and sit down!", whereas if the person selects the left-hand card, the magician says, "Fascinating! I'll hold on to this card you've selected; can you mind the other one for me, and resume your seat." Either way, the mark ends up with the predetermined card while still believing they've made a choice.
In the Goblin Guard Room, there are three exits: through a doorway to the east, a doorway to the south, and a corridor to the northwest. (The stairs to the north are where the players have just arrived from.) Despite there being three exits, an extensive sample of internet write-ups reveals almost every party goes northwest.
That's great. It's the direction the DM wants. Northwest takes the players to the Torture Chamber, and continues their journey through the goblin-themed subdivision of the keep while giving them the chance to pick up additional intelligence about what lies ahead. East would have taken them to some quite challenging caves that they may not be ready for yet, whereas southwest shortcuts about half the and progresses them straight towards Kalarel.
How does the encounter accomplish this? It plays on some basic psychology. Westerners read from top-left to bottom-right. We're trained to think of northwest as "first". Secondly, the corridor offers the path of least resistance - it's an open passage whereas the other two options are delineated by doors.
Third, it pulls at our sense of incompleteness - the doors form hard lines, whereas the passageway trails out into a blur, which is the sort of undefined state human minds gain satisfaction from resolving. Fourth, it's the nearest option - it's chosen as soon as you step into the passage, whereas heading for the theoretically equally-close door to the east requires first bypassing a cross-passage.
And fifth, the map shows stairs behind each of the doors, which suggest to players they'll be heading "deeper" by going in those directions, even though the stairs turn out to be largely aesthetic features that don't actually take players to another level of the dungeon.
Players are practically hardwired to go northwest, while at the same time thinking they've made a decision about their destination. It's like clockwork. And, in the unlikely event that they don't make that choice, a DM who doesn't want to just run with it is free to equip these other doors with locks and have their key carried by the goblin boss to the northwest.
 Was this effect deliberate? It's significantly cleverer than any of the other design in the module, so I'm tempted to think not, but the placement of the otherwise redundant stairs on the map suggests the designers may well have had this goal in mind.