One important thing is that this is not in DC, but in the suburbs. These suburbs are the richest counties in the country. There are many blacks living there, but these are middle class to upper middle class professionals. His parents were likely married with college degrees. Very different from an aspiring rapper in Chicago. This would also fit the white school shooter mold.
The odd thing is, at least one study has been done about middle class blacks, and they often seem to be affected more by black culture than middle class culture. Wish I could remember the study.