It is common problem for many "mild" (ASD level-1) autistics to be criticized as "you do not look autistic" or some of its variants. Also sometimes seen in social media that moderate autistics (level-2) (claimingly) facing similar issues to disclose their diagnosis.
By "visible" I mean the publicly considered easily observable disabilities, such as extreme intellectual disabilities, visibly heavily motor nonfunction or totally unable to move, saliva dripping from mouth, complete nonverbality or observably distorted voice and language, disfigurement or birth-defects, inability to hold urine or stool, etc. Usually the known to be severe (level-3) autistics have at least one of these "publicly perceived as disability" symptoms.
Incidentally, autism is not itself a visible condition at all, and the intellectual disability is not itself autism, its sometimes a co-morbid condition with autism but it is not identical to autism, rather autism is basically the impairment in social cognition. Also some of the symptoms of autism may be actually visible or easily observable but these are commonly mistaken as intentional inappropriate behaviour or lack of morality or as some mental illness instead of cognitive difficulties or social disablilities.
Now my question is; Is it possible that someone has level-3 (severe) autism yet on superficial look or talk the disability does not appear?
Theoretically it seems to be very possible that a severely autistic person may lack all of the publicly believed stereotype on disability, also can lack intellectual disability, moreover can apply sharp observations and observation to mask and fit-in, yet can have tremendous problem in social aspects. In such case a level-3 autistic too may face "you don't look autistic" situations. And probably all the observable symptoms will be imsinterpreted as mood or behaviour issue.
But does that happen in reality? or all of the severe (level-3) ASD have also some publicly believed stereotype of disability?
Note: See also Autism "severity" levels