Chinh,
I was wondering the same thing when I first saw this a while back and did some digging. Here is the explanation:
First of all, there are only a VERY small number of students who actually score 90% or above. This is because you have to have 90% of questions right in your FIRST attempt across ALL the questions you answer. That's hard. And second, out of that small number, an even small number actually reports back using the anonymous survey.
And so, the % you are seeing in the 90%-100% row is the feedback received from only 6 people: 4 passed in their first attempt, 1 passed in their second attempt, and 1 failed their first attempt, but then didn't go for a second attempt.
So overall, my recommendation is to ignore that particular row, because the number of students who fall into this category and then report back is so small that it's statistically not really that meaningful.