Well, every interaction – ever if there aren’t any words shared – are based on how we perceive others as well as ourselves. Because most people are capable of visually perceiving others, race is a constant entity in their mind – subconsciously at least. Therefore, people are always going to have a hint of a prejudice or racist thought when interacting.
Also, I wonder why did the kid write the note on his door himself… maybe to bring the concept of race up in a dominant “white” campus.