Non-human/supernatural lineage is surprisingly common in the universe of Smile For Me.
We know for a fact that vampires exist, although they seem to stay mostly separate from humans, going by Trencil's reaction to being exposed as one. Who's to say that other species don't exist as well? The game as a whole is an allegory for the effects of the generational cycle of abuse - and how to break it, should the player chose to do so.
Despite the main objective being to learn every Habitician's individual dilemmas and cheer them up before the Big Event, the process of actually doing so takes deliberate time and energy, as opposed to crueler or more apathetic paths. There's also the fact that while the game has a sizable cast of characters and encourages the player to spend time getting to know each of them, it's ultimately a story about Dr. Habit, a man who hails from an abusive family and in turn, has inflicted both physical and emotional harm on others in his misguided quest to find true happiness. Choose to punch him off the balcony, and you continue the cycle, or at least make it so that Habit will never find closure or try to redeem himself. Choose to give him the tooth lily, and you let him know that there is a way out of the cycle, and that his current plan was an ultimately fruitless endeavor.