I think the difference is that if an autistic person learns to mask, that's probably useful as a coping mechanism but doesn't remove the autism in the sense of making the fundamental neurological difference go away. Anxiety (even in anxiety disorders) can be fundamentally reduced by exposure therapy, not only in the sense of finding more effective coping mechanisms but in the sense of the anxiety itself diminishing or ceasing to exist.

For what it's worth, exposure therapy is a real term and it's an actual part of cognitive behavioural therapy.