The difference is, that if your ISP uses CGN, you basically sit behind another NAT router and your router will not be reachable from the Internet. With a service like portmap.io you establish a VPN connection to them and then you setup a portforwarding at their end and they route all packets through the VPN tunnel to you.
But reading your last comment, your IP from your router matches the reported IP from ipify.org. Who knows what happened earlier (browser cache?).