Facial expressions and body language (movements, direction, etc.) are approximately 2/3 of the ASL language. Hand signals and fingerspelling take up the rest - a minority of the Total Communication. You are correct that the deaf are extremely expressive in their faces - which corresponds to what goes into a good ASL interpreter.
You’re right. Unfortunately, people are ignorant when it comes to the Deaf and American Sign Language in situations like this.
And the fingerspelling is soooo fast! Amazing coordination.