No worries, it's a common question and an old bug.
Chariot Archers were in the normal combat class in the vanilla game. They are changed in GEM. A combat class is like the following: Melee, mounted, ranged (archers), siege, melee ship, ranged ship, and so on. It's not the unit type (in this case, Chariot Archer or Barbarian Hunter, also later in the game War Elephants, Keshiks, Camel Archers, and Horse Archers).
It has no effect on the unit's appearance or its base stats to change the combat class of a unit, and if its changed to an existing combat class, it will still use animations (for example, GEM moves submarines and destroyers and ironclads to different roles, and those should all still work). What it does allow is that you can set up appropriate promotions (submarines wouldn't get useless land bombardment promotions, mobile archers could get range promotions, etc), properly swap promotions when the unit is upgraded (so they don't keep useless ranged promotions as a melee unit or vice versa), and so on.
The downside of that is that we can't link a new combat class with combat animations. Since it only effects in civup submarines and mobile archers (the two combat classes that didn't exist in the vanilla game), it's kind of a minor issue versus fixing the game play issues that are otherwise involved. I think people have considered putting carriers in that list too.
