The diagnosis of Autism is given when someone meets the diagnostic criteria. If they have enough of the traits and symptoms listed in the DSM or whatever your country uses, and those traits and symptoms are strong enough to impair their daily lives, they get the diagnosis. It does not matter what caused the traits and symptoms. So if brain damage from a stroke or from anything else caused to you develop enough traits and symptoms that fit the diagnostic criteria for Autism and they impair your daily life, then yes, you can "get Autism" from a stroke or another type of brain damage. I don't believe it will work the same as with someone who was born with it from genetic factors but as long as you meet the diagnostic criteria you can get the diagnosis no matter what the cause.
Now one of the diagnostic criteria is that the traits and symptoms have to had been present in early childhood, but if you had a stroke when you were born or a baby than that would fit the criteria.
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"I'm bad and that's good. I'll never be good and that's not bad. There's no one I'd rather be than me."
Wreck It Ralph