Are you sure it is from the artist? It looks very much like the photoshop by a Konachan user to fix that issue. Only added back onto the rest of the image.
The link in the source was posted in the description of the original image on pixiv, so it should be. The source image is linked to an account with the username 電磁砲二期, which is one of the artists aliases. If it is a photoshop by someone else, it at least seems that the artist is aware of it.
