@Jeanne246
It sounds like you have already pre-approved John's enquiry, but just to clarify for the future, if it is a booking enquiry (rather than a booking request), you do not need to pre-approve nor decline it and this will not impact your acceptance rate. However, you do need to respond to it within 24 hours or your response rate will go down.
I would have responded saying, "I'm sorry, I'm just renting a room and do not get involved in my guests' personal matters." He would then have no way of booking and if he continued to message you would not be under any obligation to respond. You just have to respond to the first message within 24 hours.
Anyway, it's true that he would probably not want to book the dates anyway, but once you have approved it, he could and then he could see your address, phone number etc. Of course, if he was accessing his wife's account, he already has this information, but he could have also seen the booking confirmation for two people in her emails without having access to her Airbnb account for the full details.
I'm sure this will probably all blow over though. If the wife doesn't seem concerned about him showing up, that's a good sign.
Also, when a guest books for two people, I always ask who they are travelling with, including that person's full name.