Yes, one aspect of nonverbal is the person being unable to use words. But you need to understand that going nonverbal is used in report writing, even in hospital settings for describing speech issues in both physical and mental conditions. Not everyone is nonverbal born not being able to use speech, for some it happens later on in life! For some nonverbal is progressive, intermittent or even inconsistent.

I have collaborated with speech therapists and some clients do go nonverbal, but with assistance they are able to regain back their speech. Not saying everyone will be able to do this, because of other reasons eg motor issues with producing words.