It was referring to the traits chosen by each AI at the start of games. Previously they were 100% random which gave odd results sometimes  - an AI could have one trait to make it focus on warfare, then another to make it focus on magic. Or one that made them peaceful, and another that made them aggressive.

Now, custom sovereigns will inherit a selection of reasonable AI traits from the race they were created from.

Ah right I see, it's the AI traits / AI personality traits like "Expansionist", "Greedy", "Paranoid" etc under Leader Details in the Foreign Relations section that are (semi) randomized.   I get it.  I thought it was referring to the talents that a sovereign has (which would have been weird if they were randomized).

Cool, thanks.