There is no way to tell from just asking us on a board what could be wrong with that child. It could be FAS, it could be autism, it could be shyness. You’re describing symptoms my daughter had. She didn’t respond to noises much, wouldn’t maintain eye contact, and generally just seemed to be in world of her own. The therapists thought classic autism as soon as they met her.
During the dx process we had her hearing checked, various physical tests performed, vision screened, and a four month long psych eval before they determined autism and speech delay, only to change it six months later. You’re not going to get any good answers without a good in-depth analysis. Is his mother willing to get that started? We started at 2.5 but it took almost a year for the diagnosis to be complete. She goes to speech therapy and auditory “listening” therapy plus OT every week now and it’s made a world of difference, but let me tell ya, you have to PUSH for every appointment and every bit of information. I don’t know what education is like on a reservation, but my county/state the public school system is in charge of all those tests after age three so if finances are a problem maybe she could look into that.