I don't think there's anything wrong with the DM moving things into the path of the players without them knowing. As long as something hasn't been established yet in the fiction, the players will notice no difference. Take for example these examples:
Example 1: The players are in a dungeon and they can turn either left or right. Whatever choice they make, they encounter an ogre.
In this example the DM forces an ogre encounter on the players, but the players are unaware that their choice made no difference in regards to the ogre. However, their decision still affects where they go in the dungeon. I'm not a fan of this, because you're possibly taking away the option to not encounter the ogre. I like there to be an option to the players to avoid combat in some cases if they choose to.
Example 2: Whatever choice the players make, they encounter a library.
In this example I think the DM is robbing himself of the excitement of seeing where the players will go next. Once again, it does not affect the players. Personally I prefer fixed locations in a dungeon. This is also why I dislike it when a DM randomly rolls rooms for his dungeon. I prefer to have a sense of design coherence.
Example 3: Whatever room the players choose to search, they find an old key.
I've made use of this technique occasionally, by simply placing an item that was optional to their quest, in whatever room the players searched in. It was a simple way to make the loot more interesting. I wouldn't do it for everything, and certainly not for important items that matter to the plot. Note however that if you are running some kind of detective campaign, it can be an easy technique to get the players back on track when they are a bit lost. You just have them find a clue wherever they happen to be that gets them back on track.
Example 4: The players are exploring, the DM rolls for a random encounter. The players go north and there's a wizards tower there. Once established, this thing is now forever in this location.
I've done this numerous times during exploration. The players are in an uncharted region and choose a direction to travel in. They make a navigation check (which determines if they actually go where they intend), and then whatever encounter I rolled is there and stays there. This could be a creature or a location.