It's stupid. This calculation insofar seems to pick words at random, have a bias for scientific terms as "difficult words" and use a lot of foreign words when it wants to test your English language skill level, which all mess up the test scores. Furthermore it automatically calculates your score as better or worse if you are or aren't a native English speaker and on top of that does not test for any DEFINITIONS per se so its way of examination is not testing for active knowledge (because you only have to recognise the words and not produce them) nor does it test for passive knowledge (because you get no context).
I have linguistically debunked your plaything. There is no need to be upset.