The only way I think one could justify a "start of fall" this late is if meteorologically the fall lag was much longer than the summer or winter lags (which might be justified depending on the meteorological definition of fall).
But the fact people view the equinox as the fixed start of the season means they can't be thinking meteorologically (as then it would vary by latitude and existence of water bodies) OR astronomically (where the equinox is mid-season by definition).