I am not sure if this is specific to the mod or a feature of BtS in general, but I have noticed it in RFC where cities are commonly very close. I often have the majority of the culture on a plot (often well above 50%, going into 70 or more) and still some other neighboring civ owns it. How does it happen?
Example save attached, look at the squares around Amsterdam (the ones in French and German territory).
Example save attached, look at the squares around Amsterdam (the ones in French and German territory).