It is not a soy derivative it is an wheat gluten alternative to soy.

that this cartoon meant that a chicken had not been slaughtered for dinner and in its place was some other foodstuff seemed to me plain whether one knew what seitan is or not. I know I didn't know it, but it was an easy surmise.

Don't read too much from too little information. "Evidently it's a vegetarian place". Really? That's evident from the lack of one menu item, the inclusion of another and one wise crack? I know places that cook garden burgers on the same grill as hamburgers