It is unfortunate that you lost a tooth. However, it really depends upon how much bone was left after the roots were removed.
Typically, if the roots were removed gently and there was bone before and the tooth was removed due to Tooth decay, there is no need for a bone graft. However, in that location, the bone is not abundant and a graft is sometimes necessary. You should really ask the dentist to show you the X-ray or the CT scan and explain to you why a graft was needed. Unfortunately without any further information this is all that can be assess at this point. Best of luck.