Somehow I've managed to overlook this for years:

Compare his legs to the similar left-handed attacking sprite:

Or the normal standing animation, for that matter:

Every animation of his sprite is consistent with those, except for the normal walk animation and half of the right-handed attack animation because they share the same back leg sprite. The first thing that came to mind when I saw this was Cecil from the SFC boxart:

The unarmored legs on the walking sprite are very similar to that. The palette is obviously wrong but I think it's plausible those legs are a leftover from an earlier Cecil sprite design that mimicked this artwork, these two tiles somehow didn't get updated when everything else did.
Another interesting thing - they actually bothered to fix it in the GBA version:

Pretty half-assed fix, they just reused the legs from the left-handed attacking sprite rather than drawing a new one with the bottom outline of the hand and arm and the back of the cape. Still, got to give them credit for bothering at all.