The question has never been whether the ball rolled back into the hazard. The question is whether or not the ball was beyond the hazard margin line before it rolled back into the water. It is not uncommon to include 5 or 6 feet of usually dry ground within the margin if that happens to be where the natural break of the land leads to the water. If the ball hit within that piece of ground, then it was never outside of the marked hazard margin on the far side, and thus must be played from the point where it last entered, which was apparently right in front of the tee.
My question was actually about the interpretation of virtual certainty -- the credence to be given to a witness in the absence of personal knowledge, rather than than the precise location the ball entered the hazard. Apologies if that wasn't clear.