Quote Originally Posted by Antagonist
I suspect those "classifcations" are assigned by the game and may be hard-coded based on armour values or something, but I'm not sure. It can certainly be annoying sometimes.
The unit-class tags are moddable, and tell the game when to build the unit and where to place it in the battle-line. I can't remember how well Samnite heavies are armoured, but if it's about equal to that of the early principes, they probably shouldn't be placed in the main battle line. Ergo, they are light infantry.