7000 to 10000 is a lot of folks hacking at the ground with stones to farm.
A lot of people to feed with game.
A lot of people living in one spot.
Just building privies would be a full time job.
Which, coupled with the idea that they floated their building materials downriver from 40 miles away, suggests a rather high level of sophistication and specialization.
Also, the idea that newer houses were built on the remains of older ones, suggests to me the possibility of organized warfare, including the destruction of the older city.