I know what happened. In fact, there's no KanColle tag on Pixiv. But it has Aoba and Furutaka tags.
When uploaded here, the tag for Aoba (青葉) and Furutaka (古鷹) are recognized here but as a Kantai Collection tags (aoba_(kantai_collection) & furutaka_(kantai_collection)). Here's why there's a KanColle tag.
Both should have been instead aoba_(zhan_jian_shao_nyu) & furutaka_(zhan_jian_shao_nyu).