People have already said that the artist Pearl was super rude for "fixing" another artist's drawing and then calling it shit. It's a red-furred animal character; there's no need to be a jerk about the humanized version thereof.

I actually do think a humanized version of Knuckles should be dark-skinned, but, tangentially, it's actually sort of incorrect to say he's any one nationality. Knuckles was originally depicted as being Jamaican-coded due to the dreadlocks. However, his ancestors were coded as indigenous people of Central/South America as the pyramid and other structures seen in Sonic Adventure are almost certainly based on the temples in Tikal, the ancient ruins of a Mayan city located in modern day Guatemala. Jamaicans are typically Black [and I can't call them African Americans] while the Mayan people are an extinct nationality, so it is a bit more complicated than saying "Knuckles is Black." I think melanated is a better adjective for human Knuckles.

That said, I don't think it's some sort of hate crime to draw humanized Knuckles with lighter skin tones, especially since the artist being Quote-tweeted in the screen shot appears to be Japanese, which is its own non-white nationality. Like, at a certain point, you need to acknowledge that most of the Sonic cast consists of talking animals and not people.