Identifying as Alterhuman doesn't necessarily mean the same thing as identifying as non-human. It's an alternative way of experiencing humanity, and/or having experiences that transcend or go beyond the typically recognized human construct or stereotype of experience. This could be due to neurodivergence, plurality, feeling more connected to primal human traits, etc.
Regarding having a nonhuman identity, it's very much possible to feel nonhuman by nature and on a psychological and/or spiritual level regardless of whether one also identifies as Therian, Otherkin, or any other specific nonhuman identity. One can also have a highly complex and multifaceted experience of oneself and one's identity and identity expression, or one can simply feel nonhuman. One doesn't necessarily specifically have to have any Theriotypes or Kintypes at all to identify as nonhuman. One can feel nonhuman fundamentally and either connect this feeling with being a specific species or entity or not. It's also possible for someone to just feel like...themselves, not a certain other species, but also not exactly human.
It's very much possible to identify as or with concepts, objects, archetypes, certain phenomena, etc., and not only as or with certain species or entities. It's very much possible to feel strongly like the personification or embodiment of something. I can also see how a connection to an object could be so deep that it becomes part of you in some inextricable way.
It's possible for those in a system to feel Alterhuman because being plural is considered to be outside of the social construct of what it means to be "human," as well as the fact that some systems may contain nonhuman alters. It's also possible for one to feel Alterhuman on a deep level while having Kithtypes but not any specific Kintypes. Being Kith itself is a fundamental Alterhuman identity in its own right.
One can feel deeply nonhuman on some intangible level, either wholly or partially, or feel Alterhuman, and not involve any additional labels. It's all valid.
Some may feel as though they were always meant to be a certain very specific species in both mind and bodily form, or else one can feel as though they were meant to be more anthropomorphic. One can have multiple types and feel like their types are all separate or one can feel like a hybrid or chimera or simultaneously separate and hybridized, or one can feel like all of their types are connected through symbiotic relationships, or else one can simply be without types or have types that are fluid. One can have "unusual" types and rare types.
Being Alterhuman and/or nonhuman can mean different things for different individuals, though ultimately this experience is essential to who one is and this identity and the ways one might express it should thus be honored and respected.