Double the Cavendish

This is a photo that is current up for sale on ebay. It is really a neat photo. Here is the little story that the seller tells with the photo

While we were driving through London looking for Paul's McCartneys Office, Abbey Road Studio and other Beatle related sites I was pleasantly surprised.
There he was, walking down the street, carrying a wooden plaque.

"Hello Paul, may I take your picture?"..... "No, but I'll show it to you"

One snap with my cheap camera. "Bye" "Cheers"

What are the chances of seeing Paul walking by his London home holding a Linda McCartney photo of himself that was taken at the same place? I mean really? Why can't stuff like this happen to me?