Then what was the plan? Lure them back to Aurelia? Wouldn't it have made more sense to keep his identity, and the other messages, hidden? If Martellus hadn't revealed the existence of that space hulk and the need to go there, the larger conspiracy involving the chapter master would have remained under wraps.
I know that all of this DOES make sense if Avitus turns out to be the traitor, but CHRIST I hope this doesn't turn out to be the canon ending.