There is a portion of the loot that is from the remaining equipment from the battlefield. But not everything that drops on the field becomes loot. There is also a part of the loot that is a treasure or trading goods. Usually some food, coins, tools. You could say you are getting about 15% of the enemy parties goods if you encounter them in the world. Attacking camps give you more and better gold / treasure / misc while the equipment remains what they wore in the fight.
Any item be that armor or weapon that was destroyed will definitely not be in the loot. But if you manage not to destroy it, there is a chance it appears as loot. It might even depend on the items durability.