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If I were a betting man, I'd say Kumosuke drew it. The image on Kumosuke's pixiv is bigger and was posted before the post on Hongfire. It's fair to say the image probably didn't even exist on the net before Kumosuke put it on pixiv. It also matches Kumosuke's sketchy art style as well.

The guy on Hongfire didn't even make much of an effort to defend himself, other then posting a miniature pic of a sketch which could be anything.