You might have afterwards challenged him to read your mind and reveal another 3-digit number that you were merely thinking of. I guarantee you he would have balked.

Which is not to say that he didn't have a great trick there, if it indeed occurred exactly as you describe--though I'm inclined to think there was a little psychology employed to cause you to remember it in a way that makes it seem a little more impossible than it actually was. I know from experience that it's almost frighteningly easy to convince someone that you've caused a spoon to bend in their own hand--they can even be convinced beyond all doubt that they feel a tingling sensation as their innate psychic powers are unleashed.