I think Chris is both right and wrong, situation depending.
Where Chris is right:
Improvisation is key to being a good DM. The first casualty of any war (or adventure) is the plan. I have never run an adventure in 30 years of gaming where the players did exactly what I suspected that they would do for an entire gaming session. It never turns out exactly how I expect, although it can head in the general direction that I expect and specific planned encounters can and do occur.
It is critical that a DM improvise and it is totally reasonable for him to try to improvise the group back in the story / adventure direction that the DM planned.
And as a general rule, players should work with the DM to craft a good story.
However:
Example where he is wrong:
The PCs enter a dungeon. It closes on them so that they are trapped. They spend the next 4 gaming sessions trying to get out of the dungeon whilst the DM is trying to keep them in. He did, after all, work hard and long on his mega-dungeon.
But, the DM in his railroading attempts here is not considering the motivations of the PCs. The PCs are motivated to not be trapped. The players are roleplaying their PCs correctly in trying to escape. Once they do escape and have an escape route, they then can decide whether to re-enter the dungeon or not. However, the DM should not be overtly or subtlely attempting to get them "back on track" in this case.
Note: This situation does not need to be a dungeon. It can be any situation where the players feel strongly that their PCs should not be going down the path the DM laid down, be it an adventure, a social situation, or whatever.
The current storyline or adventure should never take precedence over the motivations of the PCs.
Story is important. No doubt about it. But, the DM's story is only one component in the entire mix. There are many players at the table, each with his or her own storyline to contribute and they have the right to express it (and influence the other players in a direction of their choice) as much or more than the DM. Typically, this does not happen to the point that it overrides the DM's current story or adventure. The DM's story tends to come out regardless. But, a good DM has to be aware of when for PC motivations of their own, the players decide to scrap the current story and go their own way, and the DM has to improvise a new story.
The social contract works both ways. IMO.