I don't think you can argue that without getting into the weeds about cultural appropriation, though.
I used to think my mom's cooking was just "Cuban", until I tried food in Spain and some of it seemed remarkably similar. Seems obvious in hindsight, my grandfather emigrated from Spain.
Then I tried food from Morocco and Egypt and found familiar stuff again, and understanding the history of these countries explains how these things might have moved around and mixed.
I don't think anybody in this thread has argued that food doesn't or can't move around between cultures. The question is, who owns it? And like a lot of other cultural products, the concept of 'ownership' seems to be most dismissed by people who don't have anything to lose.
Food is culture, and white men like Gordon Ramsay truly have nothing to lose. So when they take an ethnic minority's food, put it in a restaurant and insist that they procured it in all it's authenticity (but 3x the price), it's like an artifact they 'found' and put in a museum (even the description of this restaurant's decor sounds like they went for 'historical artifact') , and they are the ones telling its story and curating this experience as "the authentic one". That IS appropriation.
You clearly don't understand what the word authentic means in the culinary world and are assigning weight and value to it that most do not. It has nothing to do with race. It strictly refers to recipes/ingredients/flavors/techniques.
I would never refer to my Pad Kra Gao as authentic because it's not prepared in the traditional manner. If it was, I'd sure as shit promote it as an authentic recipe because it would be.
Regardless, let's consider this logically by asking questions.
1. Is Gordon Ramsay allowed to serve the cuisines of non white cultures? If the answer is no, I'll just blow out of this conversation entirely because I believe that to be a ridiculous position to take and no reasonable person would agree.
2. Assuming the answer is yes, can he not promote the food as retaining the authenticity of it's traditional recipes, ingredients and flavors? If not, and you answered yes to no. 1, then you're saying he may only serve the cuisines of other cultures if he does not produce it with authenticity? In food, that means his recipes/flavors/ingredients are not true to the original cuisine.
Do you see how ridiculous that is?