He's talking about Halo 4. That was the only one that didn't have the terminal content in-game and I remember hearing about this.

: It actually almost felt like H2A would be from the perspective of Agent
: Locke, 'reliving' the Chief's history; implied by terminal-like cutscenes.
: Sort of like how ODST played the flashbacks, the original game content
: would be the flashbacks, while the terminal content is Locke's
: storyline... *shrug* maybe not, but it seems feasible.

I've heard in one or two places there's going to be a prologue and epilogue somewhere in the mix that kind of introduce Halo 5.

: That, however, leaves Halo 3 (if completely untouched) not as relevant
: to Halo 5+ as H2A. On that note, what could be the possibility that
: they toss in some additional hidden/secret content in Halo 3? Or is it
: really going to be a direct raw port from 360 to XBO?

good questions