It must be X given that they recommend installing xbacklight, arandr, and Compton alongside it.

And the section on running in Xephyr (X server that runs inside another X session) for debugging.

Was this written by an LLM?

If you mean the comment, I think so. That's why it is probably flagged

No, it was not written by a language model (LLM). I know one of the authors, Mingzheng Wu, and have followed his work closely, including his papers on the rapid enhancement of glutamate-evoked dendritic spinogenesis in the medial prefrontal cortex through dopaminergic mechanisms, and the suppression of neuropathic pain through inhibition of YAP/TAZ activity in the spinal cord.