Some students with vision impairments when they are very young or developmentally disabled have a lot of behaviors in common with kids with autism. A good indication that a student with these types of behaviors does not have autism, is if they relate well to people, for their developmental level. If so, they probably do not have autism. To really know, you need to get an appropriate assessment, and if you don't like the answer your school district gives you, go to an outside evaluator. To make such a diagnosis really is pretty subjective, as much as educators and assessment personnel like to believe it's not.
Different assessors have different opinions.