This seems very typical of Quebec, or at least the area where I live of Quebec. Basically, people are too afraid of telling what they think in your face, so they complain to their friends in your back then eventually someone else repeats it to you.
Over here it's more common in rural areas or with older jobless people who lived with social problems and poor parental education for most of their lives. Sadly the latter group often like to start false rumors about other people or repeat things they shouldn't just to cause troubles to others and to break relationships. It isn't very looked upon over here because a lot of people do it but in many cases with teachers, for serious issues like you state if you don't complain yourself to a teacher and instead get a friend to do it, the teacher might ignore the complain in case it isn't true that you said it.
Another issue over here is if a complain is only taken into account if multiple other people complain: Basically, they'll try to get together to make their complain but they will not even bother talking when it's time to complain, only letting you do their work. As a result, the complain isn't taken into account.
