I've had some FLL/MCO-EWR flights with empties as well, including a BF 752 coming home from MCO a few months ago. The stranger that I upgraded was my PLT companion definitely enjoyed that flight. It happens some times, particularly on the more leisure-focused routes where CO has a ton of over capacity due to their competition with certain other carriers know to use the type of airplane they fly and a color in their name.
I'm not complaining at all; a $175 r/t with ~7 days adv that was upgraded on the 5day EUA both ways is just fine by me (and my clients).
S.