Huh? What else would it be? A million tonnes of white paint someone spilled? :P

Jokes aside, it's visible in every single shot of the background. There's always that greyed out haze fading the highlights and brightening the blacks. Fog is one of the better tools for giving depth to an image like that. That's another problem I have with the shot in the final trailer btw, the haze has been removed and the background now appears almost too sharp. Which I think removes some of the sense of scale.

As for greebles, I think there's plenty of the lines in the background that look like they could be rather large indentations. Not to mention the red exhaust shafts like the one luke falls into. And the move isn't particularly small either. Considering the scale of the thing, even a relatively small motion like the one you showed is a rather large distance covered fairly quickly.