he probably designed it by making a rough sketch of the whole thing with a list of all the details and equipment it has then made sketches for each peice of equipment, then made a low poly model in sketchup, then made its equipment, then cut the equipment off the main model into different smaller projects then begin retexturing the model with whatever seemed to fit, created the textures and skins, and did the same with the seperated parts, finalized the design layout, reconnected the seperate projects to the main model, readjusted the fine details, adjusted lighting and rendering, and then photoshopped it, it seems like a complicated method to work with but its actually a faster method because you cannot maintain a perfect concentration on any one model, eventually you'll start making mistakes that'll force you to have to take a break or rethink your approach in designing the model, but if you had many projects all connected to the same model to work with, you can jump quickly from one to another while the idea's are still fresh and can forget the problems you face in other stages of the model, most times its better not to beat your brain up for ideas and just let it pop in your head, that way you'll get some very impressive concepts and work-arounds for every problem you eventually face.. (or atleast thats how i do it xD) also doing this approach (with a main project and several smaller linked projects) you actually give your pc some breathing room so its not always angry at you for making it do so much lol, you'll see many professional designers using this method as well most recently in the movie transformerskaranak: your no ordinary dev-art designer +_+