You are unfortunately just seeing the quite inconclusive 129 button arrangement of an older Morino button accordion. Both potential diagonals have the same inclination and will look "correct" from the right angle, and the buttons (all of them operative by the way, making for different range limits for basses, major/minor chords, and seventh/diminished chords) fill a rectangular area rather than an oblique one.Let's suppose this is an upside-down instrument. Then the "top" is actually the bottom in the normal orientation. In what I can see in the picture (on the left) the top diagonal runs down from the outside of the instrument towards the bellows. When I place one of my accordions upside down the then top diagonal runs down from the bellows side down towards the outside. It isn't all that clear but that's what I think I am seeing.
If he were playing an Excelsior-style Morino Artiste, the photographs would tell us more.
As it is, the only clue is how he places his fingers. By the way: if you are missing the index finger, the remaining three fingers favor the non-standard diagonal, so it really begs the question why he would want to change to a different direction once he became famous enough to get personally built instruments.