It does look like patched fondant, and I would guess airbrushed with silver. You could probably get away with painting it silver instead.
That's a cool looking cake too btw!
I love it! I d say make a dark grey fondant. Cut the pieces and make the dents, then cover your cake completely w each piece. When u re done, spray all of it w silver edible spray( I got mine from michaels) then let it dry. When it s dry, I d lightly airbrush it with a grey one or two shades darker than the silver or dust it lightly w a slightly darker grey dust around the edges.