If you're saying it could be the autistic behavior is learned rather than genetic, then I agree, you'd need a twin study to rule that out conclusively. However, when people say "the autism epidemic is environmental" they usually mean vaccines or chemicals or something, not "learned from the parents."

Despite the quantity of autism research, most of it is quite bad and not that helpful on questions like this.

"Inherited" can mean "genetic" or some other method of parent-child transmission (like learning)

"Environmental" can include "parenting", but in this case the distinction is between "got it somehow from autistic-leaning parents" vs got from something else.

Also, the claim that autism might be somehow learned from parents is extraordinary and not widely claimed or supported by existing evidence. It was a discredited theory of the past though, that "cold" parenting created austism.

Also you share lots of environmental factors with your mother, like living in the same house, using the same car etc.

autism isn't adult-acquired though (literally by definition, DSM specifies that it must be present in childhood). So you'd need parent and child to share environmental factors during their respective infancies.