I'm a bit puzzled. It's obviously referencing the original Metal Gear Solid (what with Psycho Pyro screwing around with the hideo), but the music that plays after you hit 'start' and after reaching the elevator is from the VR Missions game which was a standalone dlc-esque disc that came out after MGS did.
Ah well, it gave me all sorts of warm fuzzy feels thinking about playing it as a kid on the ol' PSX...