Boulder is... special. A college town where a bunch of rich people decided to live. I've never seen a campus with so many non-students on it, just hanging out like they belong there or zipping through campus on their bikes at 40 mph. But most college towns have similar occupancy laws for neighborhoods where they want to keep students of the wrong sort out of.
Just searching "occupancy limits city" popped up the limits for Boulder, CO: https://bouldercolorado.gov/occupancy-limits