Here's a brief synopsis from that article on how these numbers came to happen.
I converted the aggregated AV for each team into an ELO rating so that I could later use that value to calculate the win probability of each team in each game this season. With the mean ELO rating set at 1500, I set the possible range of ELO values between 1320-1900, since the standard deviation of ELO ratings has traditionally been 90 points.
But ELO ratings don’t paint the whole picture, as teams who finish with worse records the previous year tend to benefit from easier schedules.