He aims to target the mid to lower part of the lat. Coiling the core while doing barbell rows may look like it is shortening your ROM, but in fact it creates more concentric focus onto the targeted muscle which hits the lats harder. This version of bb rows also eliminates supporting muscle movement that you would see in the traditional bb row method while trying to increase ROM (ie. shoulder movement/support, bicep support, trap support, etc). This is from my understanding of the movement/drill.

The point of it all has to do with running mechanics and the gate cycle. Two things: 1st- The side bend of the torso helps the hip (below the Lat he is working) to easily tilt (an anterior pelvic shift ) into a position that gives the hamstrings length to flex/tense on impact, and drive the hip into extension, propelling the body forward. 2nd- On the opposite side, flexing simultaneously with the Lat is the glute max (in posterior pelvic shift). The glutes tense hard here to over-extend the hip and get the last bit of drive off the ground behind you, right down to the whipping motion off your big toe as you finish with a leg curl like motion to complete that stride.