Some people just have very oily scalps. My son is one of them. That scalp smell is in his room and on his pillow. When he lived with me I was washing/changing his pillowcases a lot. My best friend's daughter has the same issue.
Adolescents are the worst in this regard! I remember this topic coming up many times here on the DIS when my kids were that age. I remember when my boys turned about 11 and how different their hair smelled.