I also get the feeling that the whole thing is shoehorned for the obvious purpose of being contrarian for the obvious reason that being mainstream doesn't separate you enough from the pack to sell. So: arguing that national dish IS A REAL THING would require a much more elevated level of content and research. Claim the contrary with shallow arguments mixed with "I traveled The World to experience it myself" and easy peasy, must be true because.

Other than that, National Dish is as much a thing as National Language. Take Latin / Romance languages for instance. It's something of a trope that in the old days (before modern communication and standardization of "national language" with one dialect proclaimed "the reference" and evangelized through media), going from Rome to Paris to Madrid meant every two adjacent villages would understand each other but 100 villages away this would cease to be true. Language changed so it makes just as much sense that food recipes changed.

This is brilliantly illustrated for the Balkans region by Key & Peele's sketch "Macedonian Café": https://www.youtube.com/watch?v=g1KiFON-GWg

There's "Ćevapi" as "national dish" of Bosnia, a country the size of a pea grain so sure, THEY invented it. In fact it's the exact same situation for Latin dialects. Go from Bosnia to Serbia to Romania and every two villages will make a ćevapi that's similar enough but 100 villages away the flavor and recipe would have changed enough to create the "Macedonian Café" situation :)