All this history is merely plausible, and plausibility is not proof. Things probably happened thus, though they may have happened otherwise. History, however, is by definition the search for the most probable explanations of preserved phenomena. When several explanations are possible, the historian must always choose the most probable one. But the truth is that improbable things sometimes happen. Therefore truth is necessarily stranger than history.
One could at this very point add the original dedication right now as a kind of postscript for emphasizing Smith's skepticism about his own conclusions:
For the one who knows (what actually happened in history).
This clearly is the most probable context for the opening words. All theorizing by conspiracy buffs about this being a confession of forgery on the part of Smith, a secret aside to an insider, lacks any supporting evidence in the book itself. It is only useful for those who want to believe such things. It has no place in a serious discussion of the likely probabilities. But then again if only reasonable hypotheses were allowed to be considered we would more than likely eliminate most of what has been written about the discovery - including must of my own theories.
If only all scholars were as frank and prone to self-criticism as Morton Smith ...