That's because $ip is a mIRC identifier, which, if mIRC is obtaining the IP normally inside a LAN (ie. if you're using a router) will be your LAN IP rather than your internet one. Everyone else will see your IP as provided by the IRC server, which of course only sees your public IP since from the server's point of view it has no idea there's a router or a LAN or anything else. $ip has nothing to do with what anyone else sees.
