Consider the case of photography then - would you consider photos to not be copyrightable as all the photographer did was point a camera at something and push a button? The picture was not created by the photographer - just the output of light entering the machine and hitting some photosensitive paper (or a digital sensor these days). How is that any different from you macguffin maker? Or An AI generated work?
There have been many cases for photographs though - with mixed results. Namely the line is drawn when some level of human creativity is involved in the process of creating the works in question. Like in the case where a money took a selfie - that work was not copyrightable as there was no human input into the process. Just owning the camera is not enough to claim copyright. But there are other photographs are are considered copyrightable.
The case this article talks about is more akin to the money example - someone used an AI to create an image with no human input (and he admitted to this) and tried to claim copyright on the work as part of the work for hire clause to the copyright laws. The claim was shot down because no human input was part of the process. So this image was not copywritable.
But all the articles about this case are extending the judgment to mean any ai generated work falls under the same cause. But it does not as different AI work have different amounts of human involvement in the process. The case explicitly states that those works are still open for debate.
The increased attenuation of human creativity from the actual generation of the final work will prompt challenging questions regarding how much human input is necessary to qualify the user of an AI system as an “author” of a generated work, the scope of the protection obtained over the resultant image, how to assess the originality of AI-generated works where the systems may have been trained on unknown pre-existing works, how copyright might best be used to incentivize creative works involving AI, and more.
Things are not as clear cut that the titles these articles are using imply. And if a prompt is enough, or how detailed it would need to be to claim copyright is still an open question that as far as I know has not been tested in court yet.