Artists delete their own art all the time. This is valid for Danbooru unless we know that this is a paid reward, in which case it shall be banned.
My bad, I worded that wrong. This looked similar to a Patreon reward but I wasn't sure if one of the deleted works that were public was this image or not, so I left my message and saved the post to check later on PC.
Edit: I checked with ascii2d now and the Pixiv post had a .png with too small of a difference in filesize.
