Exams be like.
I had a friend in uni that was awesome at memorising things fast and learning fast for exams. So he would study two or three days before the exam and ace it. And then three days later he didn't remember anything about the exam. While another of my friends learned things quite decently and was capable to give knowledge a practical usage, but was shit at doing exams, so she ended up failing or having pretty low scores.
That's the greatness of exams. It doesn't matter your actual skill or knowledge, just how good you are at taking exams.