If you had any common sense, you would go to the Halo: Reach forum with a question concering the Halo: Reach game. The forum is there for a reason, even if that reason is abused by many, many, many people. Anyway, Jeremiah posted a thread for discussions on rank resets. Bungie went through every reach player and checked their game history to see if they've ever AFK'd. Either your friend AFK'd, or he got reset by accident
[Edited on 05.24.2011 6:37 PM PDT]