You cannot develop autism from a traumatic experience, however there are some similar symptoms for both so one can develop autistic like symptoms after at trauma since some PTSD symptoms and autism symptoms are simular. If you have autism you would have been born with it, certainly could have been missed I wasn't diagnosed with that till I was 24...I also have PTSD on top of it as well as anxiety and depression.

I'd say PTSD can make the unpleasant aspects of autism worse, more apparent or sort of add to it. For instance its not uncommon for people with autism to get overwhelmed with what most people see as 'normal' stress like going to a store and the lights are too bright, its too loud, to chaotic and when you say that no one knows what you mean because its not bothering them...well PTSD can add to that.

Though it also sort of decreased some autistic traits, for instance I used to have special intrests in things and would do a lot of reading and research on various topics of intrest but after the PTSD it made it really hard to focus on and enjoy any of those...so that particular trait was more reduced by the PTSD while the things like being easily overwhelmed, sensative to light/noise/crowded environments and such