Unit leader is the center 1st rank unit so it wasn't him. The guys in the back don't kill too many things unlee they're getting a lanced by flanking knights in which case they turn into a spear-ma-bob. Valour is calculated per man and average per unit so if you lose most of the guys with low kills in a unit, then it'll have a tendency to climb. Retraining usually lowers it since you get 0 kill units, joining experienced units tend to keep the valour from going down.

I'm sure we've all had battled with 9 star Jedi Kataphraktoi or a King's RK unit and they lost all but the unit leader and his valour jumps by 6.

Kings, emps, and royalty in general give an automatic amount of value to the unit that killed him.