I’ve used docker for some time but always seem to get back to this same question: is the base layer or parent layer in docker an OS? I ran a python image: docker run -it --entrypoint=“bash” python:3.9, then ran cat/etc/os-release, the results “Debian GNU/Linux” . So it would seem so.
What you see in /etc/os-release is not an operating system, but a distrubution. A distribution is just a collection of files. The real operating system is “on the host” with the kernel and you can run processes in isolated environments. Even if you have files that resembles a operating system / Linux distribution, you won’t have all that you would have normally. You won’t have systemd for example. Some images don’t have any files just a single binary that has to run in that environment.