Not sure I follow. Math.random() is in testSort, so the time to generate the random numbers is part of the measurement (even though it almost certainly shouldn’t be).
Edit: my main point is that there are many flaws in this comparison, so I wouldn’t draw any conclusions from the measurements in the article. They’re pretty much meaningless.
I agree, but what I'm saying is, it only generates the numbers once and then sorts them 500 times. Yes it's a flawed measurement because it measures the generation time + 500 sorts, but the time to generate the numbers is probably minuscule compared to the sorting.
There are many more flaws, as you say, the biggest flaw is the stable vs unstable sort comparison, but it looks like the article author (not OP) has fixed it half an hour ago and updated the article.
Edit: my main point is that there are many flaws in this comparison, so I wouldn’t draw any conclusions from the measurements in the article. They’re pretty much meaningless.