I would not worry about it that much!! Really! I recall when someone gave me a 1
on one of my lessons! Oh I was P---ed!
How could they do that? But, after I calmed down, I figured the person did not know what the lesson was about or, was looking for something else, or was just being an A$$Hole!
You are a Teacher of Music! I would not take this so personal. I know you are concerned of the Quality of the lesson that you have put here but, some people just don't get it!!