If the DM is heavily leaning on them to go to the Tower of Madness and then gives them an NPC who just happens to know the way through the Impossible Maze in front of the tower and said NPC also knows how to open the door to the tower which is impossible to open, and then said NPC after being perfectly reliable and 100% necessary to get to where they are suddenly leads them to a room that slams shut behind them and tells them "now you are all my captives!" it ends up feeling a little... railroady.
It could be railroady, but I wouldn't be averse to "evil NPC tries to lure PCs to their doom" type plots. I think the important thing is that the players aren't feeling forced to go along with it for metagame reasons 'that's where the adventure is'. Personally if I have an evil PC trying to deceive the NPCs I tend to give obvious 'this guy is creepy & untrustworthy' cues and hope the players are at least paying enough attention to ask for an Insight check. Even if they fail the check I never say 'You don't trust him'; I say 'You can't read him'.