Port Forwarding - NAT Loopback - Time Warner Internet

This question is about "Port Forwarding - NAT Loopback", with Time Warner Cable internet and apps. Hello,

I'm new to Spectrum/TWC. I have their TM1602 Modem with their WiFi 802.11ac Wave 2 Router. I am trying to enable port forwarding to my raspberry pi as a small learning web project. When I configure the information and enable the port forwardind, it directs me to the Router's login page rather than the Raspberry Pi. I have other computers on my LAN and as a test, I've tried to enable port forwarding :)8080) to them. It always sends me to my router's WAN login page.

Any advice?

EDIT: See my post below, this is called NAT-Loopback. I was so confused as to what was going on and then after further testing, I finally realized what was happening. Even Spectrum's Online Support agent was confused about this issue. He knew about port-forwarding, however he thought my router was faulty and needed to be replaced.

Port Forwarding - NAT Loopback?