Not trying to be dense, but possibly succeeding: why does this indicate that Seattle's price growth is sustainable? If Seattle builds too many apartments with t

Not trying to be dense, but possibly succeeding: why does this indicate that Seattle's price growth is sustainable? If Seattle builds too many apartments with those cranes surely the growth in prices will collapse (homes seem to be supply constricted and to some degree a lack of supply has dampened demand, but this might change if condos became very affordable). Alternatively, if Seattle builds out too little then prices will grow unsustainably until they collapse to sustainable levels due to supply restricted demand dampening. So there seem to be two goldilocks zones: one where demand and supply are in harmony, and the other where they're totally out of whack and the combination of effectively liquid real estate and fluctuating value overdampen to produce stable averages with unstable individual outcomes. Which is the claim here?