The WSJ spells it out. His climbing teammates kept their mouths shut until in 2001, when during a speech he made a comment to the effect that perhaps some of his teammates had hoped neither he nor Guenther would return. That popped the cork, and several of them have since said that he left Guenther near the summit, because he was determined to descend off the west side and make history. He claims that Guenther begged to go down the at-that-time unexplored west side. But his teammates point out that if Guenther were in such bad straights (AMS), wouldn't it have been much safer to descend where their fixed lines, tents, supplies, teammates were?
There are lawsuits and counterlawsuits currently going on over several books (Messner's trying to get printings halted). This may be a bigger hoopla in the end than the Bonatti K2 dispute.