D&D is not a storytelling vehicle.
It is a role playing game.
Each of the players play the role of a Hero after some fashion.
The DM plays the role of Everyone Else.
I'd be tempted to tell the DM to go write a novel instead of playing D&D, because it seems like he wants to tell a story and not play a game.
EDIT
I've read the rest of the thread (including the DM's post), thuogh the above remains good advice for every DM.
What I point out is this:
I thought getting to their destination faster while having the city of the enemy distracted would work,
Work for what purpose? What were you trying to accomplish?
It still sounds like they were railroaded, even if you mostly went with the flow of things, there at the end. Why did the enemy have to escape? Why wouldn't the NPC help? Why did they escape in "the nick of time"?
I can understand better why you did it...it's a really common DM mistake, and some people don't even really see it that way and like to play the game that way, and you fell back on your instincts when they did something unexpected....but what work was being done? Why did the enemy need to be distracted? Why did they have to get to the destination faster?
It seems that there was a communications break down somewhere along the line where the players expected that the adventure wasn't what it was really supposed to be. The powerful NPC didn't explain it well enough, the PC's didn't have any reason to *not* risk their lives like this, etc.....
And bonus DM points for listening to the group. Bravo.