343GS said Chief was a Forerunner because: 1. Chief's got Librarian Geas sown in, the "gene song". 2. He confused his Reclaimer abilities, thus concluded he was an actual Forerunner. 3. Someone, possibly Bornstellar, tried to stop him in the past, when Chief did it, he called him Forerunner. Also why he referred to him as the original activator of the rings in Halo CE. 4. He was going rampant. 5. All of the above. As for 3, I am guessing Silentium may go over this. When Bornstellar activates the rings, it is possible 343GS may have tried to do it prematurely, and would explain why 343GS referred to John this way in CE, the Two Betrayals cutscene.