I think in this case the video is trying to measure mostly the degree of how much the artist knows what they are doing and to avoid any bias on certain art styles . That is why awkward lines was a common trait on lower levels. (the degree of success on evaluating the images shown is up to interpretation)
Is hard to measure art skill when comparing 2 completely different styles, so seeing those 2 level six can be confusing.
It also doesn`t consider the art-style flexibility an artist may have. Some may draw really glorious art in a certain style,like realism but may not be able to draw on a cartoony style.
The mostly Furry artstyle in the video is probably because these are the people that sent their art to be measured on the video????
But i agree some of the examples of art level were too confusing 