Here is a short update. I asked the Customer Service Agent at the President's Club to look into it and she and her supervisor thought it looked very strange. The more they asked me about it, the stranger they thought it was. They ended up calling the supervisors at MSY and left a message but have not heard back.
Also, she suggested that I call the WE-CARE line. So, I did. The woman on the phone was not sympathetic at all and gave me a list of things it could be:
a - a last minute air marshall
b - a last minute paid ticket
c - a plat with a higher fare class
While those are all explanations as to why the seat would have gone to someone else, I would not expect it to show that I DID get the upgrade.
Oh well, it is not that big a deal. I just don't want any hanky-panky going on! Thanks for listening.