In many/most cases, typing 'status' in the daemon will prompt the daemon to respond with "8+0" meaning that there are eight outgoing connections, and zero incoming connections. In this example, your node is receiving information only because it initiated contact with other peers on the network. Do those peers to which your node has connected have their firewall port 18080 open? If not, how are they connecting?
It seems like not forwarding port 18080 is detrimental to the decentralization of the network. Further, if port 18080 were never forwarded, then peers would never connect. Can this be right? It sounds almost insane to me, so I'm guessing I'm missing a piece of this puzzle.
If it's still on topic, I'm also curious about the unintended consequences of forwarding port 18080. Let me know if I should edit this question out and create a new question for it.