It's like the sudden change of a language style and its verbosity didn't happen recently.
To random words you pick and provide a sufficient amount of text to vary with random number without losing its meaning you need a text with high entropy.
Nothing about watermarking would require padding the response length with pseudo-intelligible Claudese. Regular filler would work fine.
Also, it would probably provide higher entropy to write normal human-sounding English instead of reusing a repetitive grab bag of load-bearing phrases. This theory doesn't really make any sense.
To random words you pick and provide a sufficient amount of text to vary with random number without losing its meaning you need a text with high entropy.