It's kind of odd that GitHub is asking people to pull an image from a Docker account that most people won't recognize (admiralawkbar/super-linter), as opposed to an official GitHub one.
But since its release, you still can't do public pulls: https://github.community/t/docker-pull-from-public-github-pa...
admiralawkbar accounts for 80% of the commits in the repository and over 98% of the code churn. I'm guessing this was a side project of his (Lucas Gravley aka admiralawkbar) and the docker image was just something that was overlooked when it became an officially advertised GitHub repo.