What Jon didn't know was that his wish had given a random person within range of the stone ten wishes. All conditions that applied to the wishing stone, in regard to making wishes (like range and changes to reality based on who hears the wishes), also applied to the person who now had ten wishes at his or her disposal.
Also, while Jon may be able to wish to know who had received the ten wishes, he could not wish that that person couldn't use his/her wishes.
But who was it that now had the opportunity to make ten wishes?
