Incorrect exam score?

[Sander-1]

I just finished the spanish exam. I did not think I did very well, but duolingo gives me a 5.00/5.0. I know for sure that I got at least one answer wrong (i said dó instead dio (dar)). Did duolingo cut me some slack by accepting that answer, and did I just do better than I thought, or is there a bug in the rating system?