I was probably too conservative. After all, half (1125) of the 2250 affordable housing units would be two- and three-bedroom units. With an average of 4.25 people per unit, that would mean 4781 people. Let's assume an average of 2.25 people for the smaller 1125 units, or 2812 people.
As for the 2250 market-rate rentals and the 2360 market-rate condos, let's assume 2.5 people per unit, as previously. That's another 11,525 people.
Of course the assumptions can be tweaked, but this set would lead to 19118 people over 22 acres. That represents 869 people per acre. There are 640 acres per square mile, so that would represent 556,160 people per square mile. That's "extreme density."