That occurred to me too. But, in Moby Dick, whale, whaled, whaler and whaling would also be four unique words.
I guess there’s not judgement on the value of the words so...
Are we are? I mean, that this guy counted Moby Dick himself rather than accepting a word count from someone else who may not have used that guideline? Because he says:
As a benchmark, I included data points for Shakespeare and Herman Melville, using the same approach (35,000 words across several plays for Shakespeare, first 35,000 of Moby Dick). I used a research methodology called token analysis to determine each artist’s vocabulary...
And so "same approach" seems to refer to the 35,000 bit, not the "token analysis" part.