Is saying "I don't understand my teacher" or "He doesn't explain well" considered backbiting?

Backbiting is to mention about your brother what he dislikes. And your statement about the aforementioned teacher is considered backbiting because he dislikes hearing such words that impugn his competence and qualifications. However, if the intention behind the statement is to complain to the administration to remove harm from you, then there is no sin upon you, because backbiting is permissible to remove injustice.