IPEX-731BA5DD06
Deity
It's because, as Obsolete said, Darius is a vassal, and as such you get full BFC in your own culture from DARIUS.
BUT the Joao, has greater Culture on the city, immediately around it, due to his cities, it was probably in danger of Culturally flipping to Joao, when Obsolete took it off Darius.
The outer Purple ring, seems to be closer to Darius cities, but the inner ring, is swamped by Joao, who'll probably culturally flip the city, if the game went on.
BUT the Joao, has greater Culture on the city, immediately around it, due to his cities, it was probably in danger of Culturally flipping to Joao, when Obsolete took it off Darius.
The outer Purple ring, seems to be closer to Darius cities, but the inner ring, is swamped by Joao, who'll probably culturally flip the city, if the game went on.