...Yeah.
My Sherlock Holmes-like powers of deduction tell me that he is left-handed and probably taught himself to play the bass on a right-handed bass, held upside down! Now whilst that may not present problems as such - if that's the way he's taught himself - surely this makes his way of playing quite unique and surely it must also be impossible for him to follow conventional tablature, music notation and exercises, etc? This would also be true of the guitarist you speak of. And surely if they tried to learn by watching other guitarists fingers on the fretboard, it would be all wrong?!!!
I just find it intriguing. Actually, my brain hurts now.