I think he's trying to describe the complexity of it, so a fairer way to characterize it might be some scripts in Python or Ruby.
But then once you added enough features that that became unmanageable, you'd write it in a proper systems language like Go, and oh, right, now you're writing Docker.
But then once you added enough features that that became unmanageable, you'd write it in a proper systems language like Go, and oh, right, now you're writing Docker.