Nonsense. In the same era when my Mopars had LH thread, none of the wheels ever came loose. Neither did any of the Chivvies or Ferds that had all right hand thread.
Funny you mention that, in theory the left handed threads made sense, in reality, not so much. Strangely, IIRC Ford put left hand threads on the left rear only in the 1980's on their F350 pickups. The only reason I know is I worked at a tire store in the 90's, and had to deal with it enough to know. We occasionally would set up the new guys and watch them try to figure out why the left rear lugs would not come off. You could not let them try for too long, since they could over tighten the lugs, or stretch the threads.