The phenomenon of tortured phrases in published papers has been going on since at least 2020 - long before LLMs were a significant factor, and certainly before watermarking their output was a consideration.

The general working theory is that these phrases are the result of a "text spinner" tool being applied to a manuscript and blindly replacing random words or phrases using a preset list of synonyms (which are often imprecise and/or inappropriate). https://arxiv.org/abs/2107.06751 found that many of the commonly observed phrases were characteristic of an online text-spinning tool.