Want to know what's the borderline between the doujins and manga in MD

[AirenxVia]

So, i found this doujin called Hololive - Tokino Sora Record that depicts Tokino Sora's journey as a vtuber. the author/artist (Purin A la Mode) which seems not from the Cover Corp/Hololive. but the original/raw itself was not posted by/in the Author owned page or self posted. But it was posted by the Sora herself who is a part of Hololive agency under the Cover Corp and each page has the Cover Corp trademark written on it that "owns" Sora. (own as owned per contract between agency and the talent). wonder why it listed as doujin and not manga instead as it can be said they owned it, but they commissioned to other author/artist?

In this case what's the borderline between doujins and manga? especially in MD categorization.
Thank you.
Ed: will move this to support forum. Cuz, i don't know where the right forum to ask. but will leave this one here