Art does not need words to express itself. It is connected with the inner self of the creator. The creator sometimes can't even put into words the meaning or significance of his or her work. Perhaps that is what is meant by the quote, "The hands can express the soul."
It makes sense that art would be able to reach those who had problems with verbal language. It speaks from the heart and to the heart.
Pottery, like other visual arts connects with those on the Autism spectrum in special ways.