I retract my previous statement - after posting, I started thinking about your rear sight leaf and it just didn't seem right. After looking again, I noticed what was nagging me about it. That's not a Russian AK/AKS rear sight leaf at all. The number style is not in the Russian style. The "1" is a dead giveaway as it's written in the Chinese style of their Type 56 rear sight leafs. So is "4" and "3," for certain.
I think either someone may have removed the original Chinese "D" battle setting character and added the Russian battle setting character; or it's one of those unexplained mysterious much like the Russian battle setting on the rear sight leafs of the Chinese NDM-86 (Dragunov SVD) rifles but with Chinese number styles.
If you're not the first, original owner of the rifle/bought it new-in-the-box, then it's hard to tell what the deal is. If you can inspect the battle setting area closely, you may be able to see whether or not that area has been ground/refinished. It's certainly an interesting issue now.