I found a mistake, that I provoke. The first time I saw the cinematic, press esc to adjust the brightness. And that sends me directly to the scene of Ben Ar and the instigators. I saw nothing that the twilight council had died.
Well, it is debatable what the protoss should and should not know.
But since they have been working with the Terran for a considerable amount of time [over a decade if my understanding about sc timeline is correct], it is possible that the protoss may have learned many things about the Terran.
Such as terran language, clothing, weaponry, food / nutrition.
Perhaps even Terran History and also Terran religion.
When two different culture co-exist and working together something like culture exchange is bound to happen.