Looks like Jaco is playing double stops in the 1st and 3rd pics and maybe a slide or just muting all the strings in n the middle one , just watched a few of his vids and looks to me like he pretty much always has his thumb on the back of the neck using finger per fret in the middle of the neck or double bass style finger1,2,4 down at the nut end
I think it would be less efficient to play those third chromatically up to the fifth then sixth up to octave lines that he did loads with his thumb over the top , I'm comfortable with calling thumb on the back of the neck orthodox good technique but also comfortable with acknowledging that anything can work and some players have idiosyncratic awkward looking technique yet have great technical facility