Not sure what you still want to hear, but here goes:
By using CtB, and bringing in Namaan from your hand, your opponent controlled your Namaan the moment it entered play. The fact that you already had a converted Namaan in play was irrelevant since you were not controlling the second one. Therefore, for the duplicate rule consideration, you controlled a Namaan and your opponent controlled a Namaan, but they were not both in Battle. This is fine.
Once the battle was over, the EC Namaan returns to the territory of the owner, which now violates the duplicate rule, so the owner chooses one to discard.