That is true. Most all Iowa "tenderloins" are cut from pork loin and not tenderloin. There are restaurants that use true tenderloins and if you look at my web site I show tutorials using both cuts of meat. The tenderloin is more tender but the difference is not all that great and the preparation makes more of a difference. The third cut of meat from the back of the hog, the pork chop, is more texturey and tougher to chew. Outside the Midwest you are probably more apt to find a pork chop sandwich then a pork loin or tenderloin sandwich.
As for Joensy's in Solon, it was (is still?) indeed closed because of roaches. I've had their sandwich and so far out of seven restaurants in Iowa that I have sampled they were by far the worst that I have had. Joensy's sign said "Biggest and Best". It was neither. Indeed it was big but the St. Olaf Tap in St. Olaf, Iowa was considerably bigger but not beaten thin.