From Merriam-Webster Collegiate dictionary:
essay - 3 a : an analytic or interpretative literary composition usually dealing with its subject from a limited or personal point of view
essay question - an examination question that requires an answer in a sentence, paragraph, or short composition
I'm not sure I see your point about the meaning of "essay."
It appears this was a test of the ability of state education administrators to write a coherent question that elicited the desired type of response. They failed. The teachers did not see the question until the moment they gave the test to their students.
My understanding is that an answer that expounded upon a single point was scored high, while an essay that listed several points was scored low.
I suppose for most fourth-grade students a "great day" in school requires several pleasing events, not just one.
Beware.
Essay 3 a : an analytic or interpretative literary composition usually dealing with its subject from a limited or personal point of view
So, those students who gave a list for a great day at school probably wrote something like, "On a great day at school I had English, and Earth Science (Save the Whales!) and Phys Ed and ..." -- that's a list, because it just gives a series of discrete items without explanation.
An essay would have been more explanatory, such as, "A few weeks ago one particular school day was truly great. In the name of the Oppressed People's of the Third World - especially the Palestinians, me and my hommies occupied the Guidance Office to demand an end to culturally biased testing." This uses complete sentences and explains what made the day great, it doesn't just tick off factoids.
The wording of the test question quite clearly called for the second form, but students who don't lack fundamental writing skills will always avoid something that complicated in favor of the first form.
Yep, and I would bet that spelling and grammar were NOT part of the grading criteria; it sounds like they graded on how well the student answered their question.