A smart man, especially someone that understands security, would foresee the argument from silence. If anything, I think it is a deliberate red herring to make suspicion fall on Szabo.
[0] http://www.gametheory.net/popular/reviews/PrincessBride.html
i think some part of nakamoto wishes to have credit for BitCoin, or at least not permit someone else to take credit - which is part of why he came out of hiding to redirect people away from dorian nakamoto. to protect him, but also to ensure that credit was not conclusively misattributed.