The term “ethnic food” is ambiguous. We tend to have a good idea of the foods on either polar extremes of the line. Despite the cultural origins on many of our favorite foods, some of them are unabashedly American now—French fries, steak, and apple pie come to mind. On the other side, foods associated with exotic locales like Thai or Ethiopian are pretty clearly ethnic. Problems occur on the line as America assimilates more and more into its mainstream cuisine. Do people consider Italian food ethnic? Maybe if you were eating sweet corn agnolotti, but spaghetti with meat sauce is about as American as it gets.
More perplexing is whether soul food is considered “ethnic.” Some aspects of soul food are reflexively American like mac ‘n’ cheese or fried chicken, but what about chitterlings and pigs’ feet? But for many Americans, especially away from the Deep South, soul food is just as foreign as pad thai.