"Medic! Get a medic over here! Redshirt just jumped on a confusion grenade and there's body parts everywhere!"
*ahem*
Yep, it's a level editor, although it's in somewhat early stages now with the initial setup screen. Functionally you can pretty much do everything, but it's not set up super clearly yet.
When you save a scenario, then later load it, you'll go directly into actually playing it. You can also load any savegame in the level editor, which I'm told Civ 5 also did although I never noticed.