Confused about Firewall

I never bothered using the firewall on my OMV as only a few open ports are accessible by port forwarding on my router.

But now i wanted to give it a try but i assume i do not really understand how it works.

I have created 2 INPUT rules for my LAN and docker networks and just forbid everthying else coming in. But that seems to shut off internet completely except for the dockers. Honestly i do not get it at all. Shouldnt outgoing internet be managed by OUTPUT rules?

root@debnas:~# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
^C
--- 8.8.8.8 ping statistics ---
2 packets transmitted, 0 received, 100% packet loss, time 1013ms

But isnt that an open socket when i initiate the outgoing request?

EDIT: just tried and you are right.