I had a similar strange experience today. Firstly, let me say that I don't facebook, twitter, etc., or any of the other "social networking" things. I do send/receive text messages on occasion from friends and family.
Today, I received what looked to be a text message from a friend of mine. The notification window contained the picture of him that I have in my contacts so I didn't bother to look at the phone number it was from. To make a long story short, we texted back and forth several times and finally figured out the sender had sent his message to the wrong number (me).
I still don't understand why my friends picture was displayed. I looked in my contacts at his entry. All phone numbers are correct, there aren't any duplicates or extra erroneous fields.
I'm puzzled by this but I've learned to look at the phone number of the sender before I respond.