From
Service and Therapy Dogs - ADA and State Rights
"It is very important to remember that Therapy Dogs do not have the same rights as handlers of Service Dogs. Handlers of Service Dogs are protected under the ADA because of the disability the handler experiences. The distinction is highly-important, and there should be no misunderstanding that it is the Person with a Disability who is the handler of the Service Dog that has rights under the ADA; not the dog. The Service Dog is allowed access based upon the rights of the person with a disability."
I don't know what a comfort tag is, but I imagine these dogs were not service dogs and therefore had no rights under ADA to be inside the restaurant. Not to mention it wasn't a very good idea to bring three large dogs inside.