Precisely. What is staggering is just that - self-teaching takes on a whole new meaning when you approach left-handed playing this way, and that exemplifies the incredible dedication and hard work which players like Sargeant and Haslip put in. Anything to just make it work, to just get a good bass line. For self-taught bassists like myself, it's very inspiring.As for the playing upside down yes you are right it is mind boggling, these people are self taught "monsters" who have had to figure out their own scales, chord shapes and even take a total different approach to the slap technique, becaused their "slap" is achieved by tapping the heavier strings with the tips of their index and middle fingers and their "pull" is achieved by pulling with the edge of their thumbs.
ITs just funny....Im left handed buy play right handed as I think that the left hand does most of the work..but more importantly that is what felt naturally to me...For some true lefties all this stuff only makes sense lefty. In stans case I bet that some righty had a bass when he was starting and it just didnt feel right so he flipped it the other way