If someone breaks the rules ignoring them is not the solution.
Danbooru is about high quality. That is high quality. This isn't high quality.
THAT is not a sketch. Its a completed piece. THAT ^ there IS a sketch and is also complete. And since when did Danbooru become a place where only "high quality" should be the holy grail of images submitted?
Take a good look at the pictures. Notice the overall good quality of them. Now compare it to the picture we have here...
Quote from the posting guidelines: "While we understand that quality can be an extremely subjective measure, our stance in keeping our gallery top notch must stand."
The uploader was too vocal at expressing his dissatisfaction. Just appeal the decision and move on next time. The moderators will do the rest for you, and it will avoid a flame war. Thanks.