Sometimes as a parent you want your child just to worry about schoolwork only. The child in turn then finds an interest they just can't stop thinking about. In this case the child started playing the guitar and is excellent at it and may actually need it for his future.
Is he doing well in school? No one knows. But as a parent I would still encourage the child in their interest especially if they are as good as this one.
Keep in mind I still want my child to do wel in school because in case this interest doesn't pan out for his future he'll have his education to fall back on.