It probably depends on the accounts, and the algorithm. If the comparison algorithm uses some sort of distance calculation between 2 users to figure out how close they are, then you could have single directional relationships.
If my comments are on an island of weirdness, you may be the closest person to me while still being really far away. If your comments are relatively normal, you might have a lot of people around who are closer than me. That would make you my doppelganger, but not make me yours.
Edit: I just checked my doppelganger (barry-cotter), and I'm not even in his list :p. I've seen that username appear in a couple other comments under this post. I wonder if there are a few super normal users that a lot of people are closest to.
My matches have each other within their top matches, but none of them have me in their top ten.
I have a lower similarity score with my top match, compared to my matches' similarity scores with their tenth closest matches. So it is that island scenario that you described.
If my comments are on an island of weirdness, you may be the closest person to me while still being really far away. If your comments are relatively normal, you might have a lot of people around who are closer than me. That would make you my doppelganger, but not make me yours.
Edit: I just checked my doppelganger (barry-cotter), and I'm not even in his list :p. I've seen that username appear in a couple other comments under this post. I wonder if there are a few super normal users that a lot of people are closest to.