Who was the old man?

The truth here is that knobody knew for sure, not even Gandalf. The only certainty was that it was not Gandalf. But given the symbolic and prophetic warning of the disguise of Saruman by Eomer, the reaction of the 3 hunters when the old man appeared, and of course, Gandalf's guess, it all pointed out to being Saruman. A clever ploy by Tolkein, to stir the reader with fear or uncertainty over a mysterious connotation. Aragorn did not stir too much on the arrival of the old man, however, as it would take much more than this to cause alarm to a Ranger, who already had enough courage to chase off the Lord of the Nazgul and 4 of his servants at night.