I appreciate you paraphrasing Dr. King there. Give that you agree with him I wanted to bring up that your thoughts on assumptions about people are a description of bigotry, which is what we would call someone holding negative assumptions about a group of people based on an attribute not relevant to the evaluation.
Racism is a systemic issue, in which people experience oppression due to their race. Because of this, while name calling may reflect racism if the target is someone from an oppressed group, name calling is not inherently racist. However, it may be bigoted if it reflects an underlying negative assumption based on Luka being white.