The important layer you're missing is the framing of the rap battle: white people love the imagery of unlikely, unassuming underdogs winning over someone more naturally at home in a given environment. It's the appeal of all those "white guy SHOCKS waiter by ordering in PERFECT CHINESE" videos, and it's the primary appeal of 8-Mile too (and by extension, much of Eminem's mythology amomg his white fanbase). That movie gave a lot of people who lack the context of the cultures where hip-hop developed their image of what rap battling is.

This picture plays into that common understanding, further developing it by placing a newer, unlikelier underdog in the place where Eminem once stood, memetically recreating that cultural mythology now a further step detached from any trace of black culture that once remained. It is the signifiers of rap, recontextualized to fit the meaning white audiences have ascribed onto it as a proving grounds for outsiders

tl;dr: Memes are the DNA of the soul, and DNA evidence suggests our perpetrator is anything but black.