Board Thread:Off Topic/@comment-23790511-20150129221847/@comment-3146930-20150130231545

If I recall, that part of the movie is told when Cortana is adrift in space after Halo 3. As Halo 4 shows, Cortana is going rampant so certain facts may be wrong. Another possibility is that during the Forerunner/Flood war, many of the AI controlled by the Forerunners were taken over by the Flood, leading to a possible corruption of data in the future.

Another thing is that during the Forerunner saga of books Andrew S-997 mentions, the higher up Forerunners were very corrupt and kept certain details away from most citizens. Most people didn't even know they were at war until the final stages of the war. As a result, the history of the Forerunners may be a case of Unreliable Narrator, with the Forerunners portraying themselves as a better race then they actually were.