Yeah - this is because your computer sees your public IP as your gateway, in your case your router.
Your router has 2 IP addresses your public IP which everyone on the internet (outside of your network) can use to get to it and view your website and your private IP which will be something like 192.168.0.1 which only computers on your network can use to get to your router. If your router detects someting from inside your network (i.e. on your networks subnet) whether it is going for your public IP or you routers internal IP it will default to your routers configuration settings rather than forwarding.
You will probably find that if you try connecting from a computer outside of your network you will have no problems (assuming all necesarry ports are open and forwarded coeerctly). To connect from inside you will need to use the local address