I suspect sentence structure is also being used or, more likely, the primary “watermark”. Similar to how you can easily identify if something is at least NOT a Yoda quote based on it having incorrect structure. Combine that with other negative patterns like the quote containing Harry Potter references instead of Star Wars, and you can start to build up a profile of trends like this statement.
By rewriting the sentence structure and altering usual wording instead of directly copying the raw output, it seems like you could defeat any current raw watermarking.
Though this hasn’t stopped Google and others in the past using bad science and stats to make unhinged entitled claims like when they added captcha problems everybody said would be “literally impossible“ for bots to solve.
What a surprise how trivial they were to automate and the data they produce can be sold for profit at the expense of mass consumer time.