I don't think it's his router. Mine shows exactly the same thing.
Interesting, not seen that before, but I have seen routers where you set a static IP in the router using PC's MAC address. I see that one has a menu tab for Lan IPv6 does that allow you to turn off/disable IPv6 for the LAN.
After reinstalling IP shows up
well that's a result, but it is odd behaviour to have an IPv6 address issued.