Art Test

Today in school one of my classes had an art test- they had to make an origami boat and frog from the 2 sheets of paper they were given. I (wrongly) assumed that if they had memorized how to fold the paper to make the items they would be given a 10 (out of 10). However, the teacher seemed to be partial to some student's frogs/boats. Even though to me they looked exactly the same some students received a 10 while other received an 8. Both of these are excellent marks as far as the Spanish standard of grading goes, but it was strange for me to witness first hand how something so similar could be graded so differently. It's art, so there is no right or wrong answer, but I guess there's more to it then just folding paper. Then again I've never been an art person so maybe I'm just missing something.