I can't speak for Mr. Goldfarb. However, my feeling is that he meant that when the film is exposed using the manufacturer's recommended ISO speed - that the film will accomodate 4-5 stops (Zones - however you want to look at it) of exposure range. The limiting factors being the film D-max and the gamma (slope) of the film's response curve.
As an example, I would suggest that anyone looking for a dramatic comparison in film response (and resultant film range), look at Kodak E-200, and Fuji Velvia. You couldn't find two more different films even though the D-max of each is almost identical.