If I had to guess, it looks like a legendary glitch involving 4 players and drop in / drop out features of the campaign's LAN feature. Of course, Halo CE only allows up to 2 players in campaign. So I'm guess that the game is getting code conflicts, from the other MCC games, somehow. It could also be a conflict with active skulls. Seeing as how Halo CE never had that option before MCC.
I'm just spit-balling here, of course.