kyle - You know, I just recalled something that happened about 9 months ago with one of my red-headed gouldian boys.
I came in one day and he had a bald spot right below his eye, around the point where the red meets the black. It extended bak to the area around his ear hole.
It was a pretty good sized bald spot, maybe nearly a centimeter square? There was no upset to the skin or surrounding feathers (so it didn't look like he'd rubbed the area, as that tends to damage/break the surrounding feathers.)
Like your guy, the bald area was totally bald - like they'd been plucked out.
I never figured out what caused it.
It stayed bald until his next moult and filled back in. It was quite odd. I never figured out what caused it. My best guess was that it was someone else plucking him, but odd to do it just once (and so thoroughly in one spot.)
It happened overnight, while he was in his cage. None of his cagemates has ever been plucky.
It hasn't happened since.
It befuddled me.
So perhaps whatever caused my guy's mystery spot is the same as what caused yours. It's been a mystery that's bothered me for a while!