How is it possible to function well but still have autism?

My male cousin has job (he's a supervisor), has a relationship, owns a house, drive and can manage himself well in social situations to the point it's practically unnoticed.

He's just sensitive to extremely crowded, too much light or loud places. It's only been a couple years since two different facilities diagnosed him with the same things; Asperger syndrome.

How is it possible to function good in society and have a relationship (the woman is aware about it but ok with it) but still have autism?

Updates
+1 y
The irony is he can recognize the symptoms and can correct himself. For instance he used to interrupt during conversations a lot in the past or not always look you in the eyes but now he controls that and he looks you in the eye.
How is it possible to function well but still have autism?
Post Opinion