: Chief hasn't set foot on Earth yet. He blew up the Didact's ship, and Lasky
: and a few crewmembers on Infinity saw him, but the general public has no
: idea he's there. I assume S-IV is still top secret or something, so they
: can know about him without anyone else having any idea. If Osman is still
: in charge of ONI, she'll want to keep Chief's survival a secret, and the
: Believe campaign still fits there.
Considering that Halsey was still unaware of Chief's survival six months after Halo 4, it's plausible.