He's also describing hotels, and aparthostels, and officers' quarters on a ship and bunch of other stuff. The devil is in the details - specifically, how much it costs to rent per sqm, and what stops the price from going up to the point it forces multiple people to share the room? What stops the landlords from subdividing the rooms further and renting them out apiece? What stops already shoddy construction from getting even worse?

Those are the big challenges of housing. Not just how many units there are, but what they are, and how much the "how many" is plain cheating.