Simple doesn't mean overhyped or over used. Both 'ls' and 'cd' are simple to implement. The script is more of a tutorial than it is making fun of anything. You'd need to give better reasons for why Docker is overhyped than "look at this simple script which does some Docker-like stuff".
If docker is overused, what would you suggest instead?
For many cases, you don't need it. For example, deploying a Go binary. Some people have the habit of dockerizing everything at any cost and complexity.
You can still stick a single binary in a container. (Putting a whole Linux in the container as well, that's probably overkill. And alas, it's also what docker does by default.)
There are ready-made no-distro base images where you can stick a single binary and reap the benefits of isolation.