As teacher I have always objected to the very idea of quizzes, as these in my opinion often mean the American style quiz where the pupil ticks of the most appropriate answer of three or four possiblities. This has in my opinion no value at all in helping me, the teacher, gain an insight into what, if anything, a pupil has understood and remembered in my classes.
Not having seen this particular quizz, I don't know if it was of this type, but I suspect it was, as such a paper can be corrected quickly and the results easily converted into percentages that look good, teachers hope, in reports to the educational authorities.
Which explains why they are increasingly being used.
There is nothing educational about them, and the very thought of a teacher giving detention for a mark of 80% is disgusting. A child who has been off sick and still gets 80% deserves praise, not punishment.
No child should be punished for doing less well than he or she could, or others in the class do, unless the teacher knows and can prove (which you rarely can) that the mistakes were not due to incomprehension of the subject, but made deliberately out of sheer naughtiness and a desire to be provoking. This CAN happen, but is rare.
I am also shocked at a teacher who makes no allowances for children being off school sick. After all this can and does happen to us all.
Unless you are the child's guardian, you should not try to discuss this with the school, but in your place, I would advise his parents to complain about this unfair and frankly quite wrong way of treating a child.