I'm not sure what it means to not be able to help faking something. To my knowledge even factitious disorders are choices, motivated by a desire to be a medical patient - except Munchausen by proxy, in which the caretaker tries to make their dependent appear disordered, but I wouldn't call that faking. It is irrational to punish anyone for something they did not decide to do, and even if they did choose to do something wrong, it is better to address their reasons for doing so than to enact retribution.

Anyway, I can't say I have experience with people faking autism. Being honestly wrong about having it is more common, so I tend to assume that people playing up stereotyped traits of autism or another disorder are in that category, unless it is proven that they know they aren't autistic.