This upload was listed as the parent post since it's of a slightly larger file size than the pixiv post by comparison (despite the image dimensions being the same).
This upload was listed as the parent post since it's of a slightly larger file size than the pixiv post by comparison (despite the image dimensions being the same).
The difference in file size is due to twitter stripping the metadata and resaving the image. In this case, the pixiv version is the most original and should be the parent. Please see the "Choosing the Best Parent" section of help:post_relationships.