An environmental factor is what have an influence on a human. For an easy example, the noise of a car is an environmental factor for noise hypersensitivity. Other example outside of Autism, pollution is an environmental factor for cancer.
For some autistics, being with friends is a factor to mask. Environmental factors influence your energy capacities, your behaviors, etc. this have an influence on your logic capacities. For example, an autistic has noise hypersensitivity. The noise in the classroom will have an influence on the cognitive capacities (like logic).
I just read this by Kieran Rose and it made me think about what you wrote:
So much of the autism narrative is a lack of reflective practice and critical thinking on the part of non-Autistic observers with all the power.