The guy from the first place seems almost bemused that she is interviewing him and tracing the origen of this fascinating and unique product. His biggest seller? Why the ham and cheese, of course.
(I remember in the late 80s seeing the ham and cheese version called the "Carlitos". I've not come across that name more recently. According to AI, it's a common name in Rosario for the sandwich, so perhaps the ones I remember were sold here by expat Rosariños.)