No, he did not "pick up" that address. Google won't issue a second address that matches the concatenation of the characters without dots. So, if I have [email protected], Google will not issue anyone else johnsmith@, j.ohnsmith@, [email protected] or any other combination to another user.

What does often happen is that people FORGET what their actual email address is when they hand it out to other people or write it down on forms. Or their friends or family mis-remember it. Your doppleganger may have actually been issued the address johnny.smith, or smith.johnny, but just forgets.