Gave it a try and got 78 correct out of 100, so it extrapolated it to me knowing about 55k+ words and saying most native speakers only get 15k - 35k...Interesting

Mine was very similar.

Given this ... https://news.ycombinator.com/item?id=48603397 ... I now wonder if the actual corrected estimate from it is even higher at 110K+, which would seem further off.