With the integration of Facebook data as links within the Contacts, sometimes the same person may appear twice, for instance if their FB name is different in some way from the name you have used.
Cards can be merged in Cards>'Merge and link selected cards' or Shift+Cmd+| Maybe you have accidently pushed these keys.
In any case, I would make an archive file of your existing contacts using File>Export>Contacts Archive before attempting any remedial work.
Do you have Time Machine backup?
I do not have any of the social media features enabled but I guess that does not mean they have not been at some point. I am still pretty new new the Macs and I shy away from any Shft Cmd and Cntrl sequences because I do not know what is what but indeed I may have fat-fingered a key here or there. Funny thing is that these two contacts were added the first and only time I have had a need to call them. I have never even looked at their address cards since entering them over a year ago.
I do have a time machine backup and I may take a look to see how far back I have to go to find the unaltered cards. Maybe based on that I can figure out what changes were in play.
To find your backup of your contacts, hold down the option key while using the Finder “Go To Folder” command. Enter ~/Library/Application Support/AddressBook. That will take you to a folder in your user library. Then enter Time Machine with the folder highlighted.
If you prefer to make your user library permanently visible, use the Terminal command found below.
You might want to bookmark the command. I had to use it again after I installed 10.8.4. I have also been informed that if you drag the user library to Finder it will remain visible.