The 2nd unit on the tile was I think a worker of some sort. If you look you'll see there was a construction option to build a Citadel. EDIT: OK, had a closer look at the 2nd unit on the tile is actually a Great General.
I really like the combat from what I've seen, It looks alot better then Civ IV. I really did'nt like It in IV, I preffered Culture Victory. However I might actually want to build an army this time and kick some butt! :)