Is it known how exactly the level generation works in this game?

The FAQ says it generates a level based on how many players there are when the game is initially created. But on a review I saw, it says the game's world is the same every time.

So what exactly is different? What generation occurs? Is it only the room areas that change (or not?) Does anything about the map change based on the players (or any other factors?) Or are there only 3 different versions of the game (one with 2p, one with 3p, and one with 4+ players?)

For example: If I start a game with 2 people, then I start another game with 2 people and the same settings, will both games feature identical worlds all the way down to each puzzle, or are some aspects of puzzles or terrain going to be different?