I think what they were referring to was specifically the reason why the N motion in the low level vortex has taken place. By this I am assuming the disturbance NE has some lowered pressure and is causing some weakness in that vicinity, drawing the vortex polarward as an indirect influence.

It was an interesting supposition on their part, and though I do not have all the tools they do for their analysis, from here it really does appear to be shear as the primary reason for the decoupling its self. The mid and high level wind overlays clearly show 15-25kts flags incurring upon the eastern semi-circle from the E and ENE.