This. Was also super confused when I saw the post. Like every docker guide literally screams at you when you use rootfull docker. Either add yourself to the docker group with `newgrp` for a termimal session or use rootless docker.
You add yourself to the docker group to be able to use the socket. By default, a uid 0 on a docker container is run as root, regardless of the uid of the owner of the container. That is precisely the issue being discussed.