Aliette de Bodard, a Vietnamese-French award winning sci-fi and fantasy author, made some valid points on the question of what constitutes 'authentic' food on her blog. These excerpts give you the flavor, pun intended, of her observations:

"What makes an authentic recipe? What is and is not an acceptable variant? [1] How should a cuisine as a whole be judged? Because truth is, like cultures, cuisines merge and adapt, and evolve. Sometimes, they adapt because they don’t have basic ingredients: there’s a very cute Vietnamese cookbook in French, Le Chant du Riz Pilé (Song of Crushed/Ground Rice), which makes do without half the Vietnamese staples, because it’s an old book and those staples weren’t available in France at the time." 
... "In the specific case of immigrants, new dishes become created, whether for the diaspora or for a foreign audience: General Tsao’s Chicken is a pretty good example of a typical Chinese-American dish that you won’t find in Chinese restaurants in France (and, if Wikipedia is correct, which isn’t always the case, a dish that the Chinese in China didn’t much appreciate)."
..."There’s also the “restaurant effect”: restaurants tend to serve festive food that you can’t make at home; therefore, most people’s perception of foreign cuisines is really skewed, because the signature dishes tend to be extravagant dishes that are only served for feasts. One good example in France is chả giò, fried rolls, which everyone associates with Vietnamese cuisine in spite of the fact that it’s hardly part of an every day Vietnamese meal."