I'm telling you right now bro. That number takes into account exploration time and everything.
The only set game time is the average time it takes to complete both main questlines.
They combine them. So very short questlines, but all the things to explore and the time you take to do your own thing COULD possibly take you 40 hours or more if you choose it. But they did not add 40 hours worth of quests. I can guarantee you that, because that is a ridiculous amount of quests.
Well, how exactly does one measure it? I don't really think there is an official way to measure it. What if you sneak through dungeons and strategically plan out how you're going to take out individual groups of enemies? What if you waltz on in and just bash everything in the face and rush through it? Then you find that one player finished the dungeon in 5 minutes while the other took 30 minutes. How
exactly do you accurately measure the hours of content? It's highly subjective, like I said.
Todd Howard was very vague with his "10-20 hours of content" statement, and people either took it too literal, or tore the statement to pieces and assumed things about it. The only way to really know is just to wait for the release. Also, IIRC you were in the beta forums as well so I assume you are basing your statements off how long it took you to complete the DLC. Keep in mind that how fast you played through it has no true meaning because everybody plays differently and at different speeds, or takes different approaches, etc.