When the game came out, the Overmind's vision was basically seen as actual future precognition. Then in a Q&A that came out during the HoTS era, Blizzard (Brian Kindregan HoTS lead writer) said that it was literally just the Overmind piecing information together and constructing a scenario from reading Amon's mind. Then presumably, Zeratul added his own knowledge to the vision since there are protoss characters in it that the Overmind has never met.
But then in LoTV we see Artanis and Amon reusing the same exact lines like "As I was your beginning-so shall I be your end." and Artanis gives a nearly identical variation of his speech:
WoL: My brethren, hear me! For there is little time left. All that remains of our race, our civilization, are those that stand beside you now.
LoTV: My Brethren, hear me! For there is little time left. All that remains of our race, our civilization, are those that stand beside you now, and those corrupted on the surface below.So wtf really was this?WoL: Trust in each other. Strike as one will! Let our last stand burn a memory so bright, we will be remembered forever! En taro Tassadar!
LoTV: Trust in each other in the fight ahead. Strike as one will! Let our last stand burn a memory so bright that we will be known throughout eternity! En Taro Adun! En Taro Tassadar! En Taro Zeratul!