If yaw to the left occurred simultaneous with initiation of gear retraction, it could support the power lever migration theory.
However, the aircraft was veering left from the moment it became airborne and the gear was not selected up. Unless the pilot was in the habit of taking his hand off the power levers at V1 (as some do), this theory is less probable than the mis-set trim cause quoted by the ATSB.
Was the pilot trained to take hand off throttles at V1? Perhaps when he had to go back for re-education after his earlier incident, someone indoctrinated him in this change to usual light twin practice. Some CASA 'experts' may even insist on this - does anyone have any experience of this?
As Capt Ramrod says, there is no need to do that. However, some would have been trained to remove hand at V1, but one would hope that any training in that concept would also have been quite rigorous about use of checklists, including setting throttle friction.