Every creatable thing is described by data, not code. There's a crazy-big database of all the traits everything has. On the graphics side, this game would have been impossible were it not for the flat 3D 'sprites', which enable the minimization of the amount of graphical assets required.
BiggerJ, I get that, I'm wondering more how they came up with data and illustrations for basically anything you can think of. It looks like your answer that didn't thread into this confirms my suspicion that it was someone just powering through a dictionary. It just seems like a crazy amount of effort to make sprites, animations, stats, etc for everything and that doesn't even necessarily address the interactions between different items.