See any explanation of what a linux container is[0]. Containers in linux are a patchwork of various features that "contain" a process group in different ways while sharing the kernel with the rest of the system.

Running either of

    docker run --rm --entrypoint /bin/uname alpine:latest -a

or

    uname -a

gives you the same kernel version. The only difference will be in the hostname.

[0]: https://embeddedbits.org/introduction-linux-containers/