True. In this case having a separate (hardware) firewall, a vpn setup or some other networking, protects you against this. That is poorly documented on Docker too.

Yet, what Docker does is still wrong: it should not disable Ubuntu's default security. Ever. Even if that security is inadequate. An analogy would be to say "While watering your plants last night, I left all your windows open. Now your stuff is stolen. I did this because you should have installed window grills: without window grills your security sucks anyway."