Docker docs:
Docker routes container traffic in the nat table, which means that packets are diverted before it reaches the INPUT and OUTPUT chains that ufw uses. Packets are routed before the firewall rules can be applied, effectively ignoring your firewall configuration.
You're forgetting the part where they had an option to disable this fuckery, and then proceeded to move it twice - exposing containers to everyone by default.
I had to clean up compromised services twice because of it.