It's clearly a Chiang painting, and he was the one who used that type of uniform in other paintings before. He also had less stuff used in AOTC than in TPM, and didn't work on ROTS at all. I heard somewhere online (so take it with a grain of salt) that he was a bit frustrated that the design aesthetics of the prequel movies were moving farther from what he established in TPM/what his work looks like. He might have used this design just because he felt it looked better, even though it wouldn't get used. And/or, because it's viewed from the back here, it's hard to tell if this is truly a different design for the Jedi uniform or is just a Chiang-ized stylization of it.