It's pretty obvious that at least one of the players, and probably the DM, is spoiling for a first edition styled dungeon crawl. My guess is probably Boromir or Legolas - and the DM figures that leading the players towards a dwarf thing will make Gimli happy, since he's the heavy roleplayer of the group and they haven't run into any other dwarves. Pretty much everything at that point is engineered to make sure they head towards Moria. It's the direction the DM actually mapped out prior to the session - he hasn't yet statted out the Uruk-Hai and has no idea what Rohan is like yet.
Since Gandalf is an NPC, the DM doesn't want to have him figure out the Doors of Durin, and decides to make that one a challenge for the PCs instead. That's the point where the players decide to focus on pretty much everything else - smoking pipeweed as an in-character action, obsessing about whether they can actually take the pack-pony into the dungeon, and fiddling with the lake. The players have just about resolved to go to White Castle or Taco Bell by the time Frodo realizes he can make an Int check to crack the riddle.
At this point most of the players do a very player thing and decide to chicken out rather than risk TPK against a population of over 500 very well armed goblins. Only the appearance of the Watcher in the Well gets them to stop arguing about how many goblins there are and whether they can take 'em, because the DM's smart enough to realize that all the players take action when Frodo's threatened.
I did say that Gimli was the roleplayer of the group, right? He's sobbing and breaking down and talking about dwarf stuff all over the place. Meanwhile, Aragorn and the hobbits are perfectly happy to play this one as a stealth adventure, having insisted there's no way they can fight over 500 goblins, and that's probably why Legolas and Boromir are the guys who wanted the dungeon crawl - they're the people who don't have Hide or Move Silently as class skills. They've been spoiling for action this whole time, vocally. The DM trying to engineer a combat to make them happy, is the only reason I can think of that a halfling with at least 18 Dex would screw up fiddling with a dwarf corpse.
"But I checked for traps already, and you said there weren't any traps!"
"There weren't. The corpse was just chained to a bucket, and leaning over a very deep well."
"Can I make a Disable Device check to get rid of the bucket?"
And in fact, Boromir probably has uttered the fateful words, within the DM's earshot...
"Awwww, come on man! They're just goblins! I mean, probably some of them have some levels in Rogue or Barbarian, but we can take 'em!"
Needless to say, he's overjoyed when a cave troll shows up.