Contradicting the teachers!

When it comes to the note Alex's parents recieved, Im confused on it. I don't understand why the teacher would tell the class a lie? Than to top it off write Alex the note saying that he disagreed with the teacher so it shows "blatant disregard for authority." Im not sure where this teacher was going with this? If a student knows the correct answer to what the teacher has written than why wouldn't they speak up? If it was me in his shoes I would have said something. In the past I have told a teacher that their information was wrong. They never freaked out on me and definatly never wrote a note to my parents telling them they basically raised me wrong. It looks bad on this teacher part.