Is saying, "So-and-so's academic performance is not good," considered backbiting, especially if the speaker does not know whether or not the person dislikes others talking about him in that way?

If the statement is made about a person without a reason or necessity, it is considered backbiting (gheebah), for the Prophet, peace and blessings be upon him, said: "Backbiting is your mention of your brother in a way he dislikes." So, if what is said about him is true, you have backbitten him; and if it is not true, you have slandered him. However, if there is a need for it, such as answering someone who asks about him for employment or teaching, then it is not considered backbiting. A Muslim must guard his tongue from that which is of no benefit.