Civs might have multiple historical paths. I wouldn't be surprised if Rome could evolve into the Normans or Byzantium or say, Spain or the Holy Roman Empire. In fact, didn't they explicitly say in the stream that there were multiple historical paths towards certain civs, with the (theoretical, they stressed) examples of the Gauls or Franks as other precursors to the Normans.
Also, I'm hoping that there will be an option to allow us to switch off historical civ preference for AI. I do fully agree with it being on by default, but both should be an option imo.