Fuck... I'm an idiot... I get it now.
Wait, actually, now I'm not so sure I do. At first I thought it was just because I was seeing it as a nut attached to the lower assembly, which would mean I was turning it to the left to loosen, which is correct (at least in every case I've ever seen)... then I realized that it was on the mirror assembly, in which case I would need to turn it the opposite direction to loosen. But now that I have it off (thank god), I'm realizing that it's actually a case where you spin the nut to the left to tighten it on the screw, and right to loosen. I've never seen this before... I take it this is fairly common, but is there a reason for doing this, besides to fuck with newbs like me?