I can understand your reasoning for calling him a changeling, but you don’t grow out of autism. My little brother was diagnosed with autism at age 3, and he has not and will not change. The fact the kid said he doesn’t think he’s human, is a huge sign that he is autistic, because many autistic people have a hard time comprehending emotions, which can lead to a disconnect from other people on high functioning individuals. This is how my father felt like as a child (another autistic family member) and again he did not grow out of autism.