Are Minecraft commands copyrighted

Depending on if the creator wants it private or not, No. According to Creative Commons which is what these commands are apart of, You can take/Edit any thing made by the creator but must credit the original creator.

When it comes to software, especially very small snippets, copyright (for the creator of the generator) might not even apply.

There's only so many ways of writing down the same command. Sometimes even just one. Anything that contains less than 140 or so bits of expression is simply too short to be eligible (due to the birthday paradox, there's a very good chance two people write the same thing by sheer accident without even having heard/seen eachother's work). Or there may be only one way of writing something. Say, the array of items in a chest. The specific combination of items in your example is your creative work, all the generator did was put brackets around it in a certain predefined way.

You can see it in the same vein as Adobe holding no copyright over the content of a PDF document, or Knuth having no copyright over a particular piece of C or LaTeX code. There's no expression involved, only syntax.