Yes I've seen that study, it had been posted on this same forum in the past. It is also a 1961 study, so I would not take it as the last word on the matter.
Regardless of the density per area (which of course can depend on how edifices are clustered more than by the number of people per building), an average of 7-10 people per building, even counting warehouse etc., still seems very low for anything that is not a modern day american suburbia.