You did not say whether your friends dog provides assistance to him.

This can be confusing to people and cause a misunderstanding of the difference between a Service Dog and a Therapy Dog.

A Therapy Dog is a dog that is allowed to go to hospitals, convalescent centers and Hospices to comfort the patients. That's their primary purpose, to help others. This is wonderful, rewarding, and honorable, but as they are not necessary for the owners health and needs, they are not allowed in public venues outside of those type facilities. They are used as a comfort to others, so encouraged to interact with people.

Guide/ Mobility Dogs are Service Dogs. They are specially trained to assist their owner with their owners needs, and are necessary for their owners health and well being. I personally trained my own Service Dog (or else, she trained me, I haven't figured that part out yet). She is state licensed as a Service Dog.
She knows when my attacks are coming on and alerts me. She picks things up for me, and helps me stand up as needed. She also assists me with stairs and knows and assists me if I go into an anxiety attack.

While Therapy Dogs are encouraged to socialize and interact with others (to comfort people) Service Dogs are necessary for their owners well being and should NEVER be spoken to or distracted by others.