Autigender, or autismgender, is a neurogender which can only be understood in the context of being autistic or when one's autism greatly affects one's gender or how one experiences gender. Autigender is not autism as a gender, but rather is a gender that if so heavily influenced by autism that one's gender and autism cannot be unlinked. There are many studies that show that autistic people are more likely to be transgender. Since gender is a social construct created by allistics and neurotypicals, and social constructs are one thing that autistic people generally struggle with there are many who may feel like their autism influences their experience of gender enough to identify with this gender.
Not all autistic people identify as autigender, only those whose gender is influenced by them being autistic. Autigender is an exclusive gender as, obviously, non-autistic people can not be autigender, because they have no autism to influence their gender.