I think you mis-interpreted what he said. He was basically saying that in order to announce the game via GI, Bethesda has to provide a lot of details on the game in order to flesh out a complete cover story. Whereas, announcing the game via E3, all they really have to do is walk up on stage and say "Hey, we're making TES V." Providing these details on the game (via GI announcement) gives the impression that the game is further along in development which would imply an earlier release date than if they provided no details at all (via E3 announcement).
Either way, I still think it'll be 1 year+ from announcement to release and I'm almost positive we'll get some form of indication of the announcement (probably on elderscrolls.com) prior to the August GI issue.