Just to be precise, autism has a behavioral component, to be sure, but there really is no such thing as "behaviorally autistic." One is on the spectrum, or one is not. However, I will agree that parenting does play a large role in how an autistic child behaves, and it behooves parents to learn the basics of applied behavioral analysis and implement positive behavioral reinforcements, since those have shown to have the best results.
As to the causes of autism, there is an organic component, and I am also convinced that there is a genetic predisposition that needs to exist. But since autism can manifest either from birth or occur as a regressive disorder, it remains to be seen what might trigger that genetic predisposition.
(And apologies for hijacking the thread with my foray onto my soapbox...)