However, like you, I have no idea at all what a "PTSD" dog is - or what it's supposed to do.
A genuine 'PTSD' dog can pick up on the subtle queues that their owner is about to have an incident.
A properly trained animal is wildly expensive and typically provided by 3rd party organanizations. You can guarantee that for every genuine one there are several people that just claim their mutt is one to bring it into the restaurant.