While it did get unintentionally leaked through the SAG just a few days ago, it appears that the animated show in question is indeed real and coming to fans next year. Legends of the Guild is being worked on by both Capcom and Pure Imaginations while being written by Joshua Fine who also worked on Ultimate Spider-Man. Production is planned to be completed in the winter and see release globally in 2019. The special is planned to be 3D animated and follow the story of a young hunter on a quest to prove himself while saving a village from an Elder Dragon. Concept art for the special includes the title text and an image of a hunter facing down a Nerscylla.
Monster Hunter: Legends of the Guild is planning to release in 2019. Check out the concept art below: