Garbage man is not equal to garbage. Garbage is bad. Garbage man is a guy who clean up the mess--he cleans up boards, gets put backs, and hits first on defense near-violently. Though he was a more complete player than JUST that, That is Jeff Adrien in a nutshell. That's what he stood for and was recruited here for.
Adrien was higher rated bc of his offensive skill set, but diarra can learn. It is going to be extremely difficult at his size, so one move and one counter will be his goal.
Diarra has said in interviews he knows his job is defense and boards. KO is probably not using the words "garbage man," but it's obvious the kid knows his role.