I believe there is an error in the calculation. I didn't use any mods. I have tried to create the biggest city possible by making every single tile with flood plain, river and wheat. Currently, it's at 75 and still growing.
Each of the tile has 10 food (don't ask me why, I didn't mod). That will give us a potential city size of 10 x 20 + 5 x 1 = 102. That is not counting adding Great Merchant super specialist (which adds one food to your city).
Having said that, health is a major issue that will eat away some of the food. Unhealthiness is at a whopping -77 vs health at 42 for my game. Hence, 35 food are eating away giving a possible city size of
205-35 = 170/2 = 85
We need more health inducing techs, people, buildings and wonders