Seriously. I don't know where you'd buy something like that outside of a costume shop, so he must've gotten it in his temple when he showed up.

[It happens: there'd been traditional clothing in his and Sakura's temple, even if he'd gone out to buy himself more Western outfits once he'd been here a few days.]

Ma'at's not supposed to have anything to do with the sun, right?

[So it's just a heavenly prank...]