Thatched roof description says it's a floor

When I go into the build menu and go over to the ‘thatched roof’ option, it says the result is: “Floor consisting of a finely mixed earth that has been tamped down.”
I’m pretty dang certain that isn’t the definition of a thatched roof. Which one is correct? The description/result or the label?

The game treats a roof construction as a containing structure of of a tile, as a layer of abstraction due to the game engine (I believe). In the game play sense, think of it as your character building a thatched roof, and making a tamped earth floor underneath it at the same time.