Are course evaluation forms REALLY confidential? Someone I know has recently submitted a course evaluation form in which he complained about how poorly the unit was organized and that the lecturer didn't seem to be well prepared for the class. Following the day this course evaluation form was submitted, the lecturer decided to revise the mark he has received for his final project and marked him down. Is this an odd coincidence or are course evaluations not really confidential?
Whether evaluations are anonymous (see StrongBad's answer for the difference with confidential, which evaluations are rarely) depends on your institution. On my university, they are. However, especially in small classes you can often get a pretty good idea of who wrote something depending on writing style and typical spelling mistakes.

But as Elizabeth Henning says in the comments, it's unlikely that this is the case here. It takes time before the evaluation is sent to the teacher. On my university, this happens only after all grades have been sent to the administration, after which it is possible to change them, but all those changes are logged - it may even be disallowed to mark someone down in that phase. In any case, the instructor won't care enough about the grade to change it and risk all kinds of trouble.