Has the Champions League gone to the Swiss System in your save?
Once the CL enters the Swiss System, some leagues can get additional CL places from elsewhere, such as coefficient rankings and league ratings, it's a rather complex system, but this would explain how Man Utd got a CL place from 5th and as you say, City got there's from winning the Europa League.
Shout-out to your friend for winning the league with Forest Green BTW.