The research nerd here. The hot dog is a sandwich. MIght add, mustard belongs on a hot dog. Case closed as Mike would say.

Quote from below sourse (Tasting Table):

Few dishes have a format as straightforward as a sandwich. At its most fundamental, it's as simple as cooking gets — ready-to-eat foods like cured meats, cheese, and vegetables placed between two slices of bread. Yet, take a gander at sandwich recipes, and it's clear how many renditions can be attributed to such a template. The filling can be an elaborate cooked food, like sautéed fish or fried chicken. The doughy vessels can encompass dozens of bread types, although most maintain they should be of the leavened variety.

Many of the sandwich classics are undisputed — no one's gonna claim that a Reuben or sweet and savory club sandwich doesn't belong to the category. However, if you start to stray from the most quintessential examples, the definition becomes more controversial. According to the dictionary, hot dogs are sandwiches, although the National Hot Dog and Sausage Council proposes they've evolved out of the term, and Anthony Bourdain similarly took a stand on the hot dog sandwich debate.

Read More: www.tastingtable.com/.../

Hot Dog is in its own category! Not a sandwich!