Sounds like a classic FAM case to me.

Flying as much as I do I know their patterns (anyone that's remotely observent can figure it out), but in the interest of not being blacklisted by the Fed. Gov't. I'm not going to post more.

What probably happened is the couple that occupied your seats were moved there to accommodate the FAM seating. They weren't the FAM's themselves, but were just asked if they minded moving from row 3 to row 2 (or whatever the case was) and they said "sure".

Why it was you that was downgraded and not them? Not sure what formula VX uses. Could be fare paid, could be time of check-in, YTD EQM's, whatever. Or it could just be bad luck.