What genuinely belongs to one place is small. It is also, almost every time, smaller than a dish.
Athens is four things, not one
Athens is where the instinct fails first, because its street food looks like a single category and is nothing of the kind.
Koulouri is a sesame bread ring sold off a morning cart — a thing eaten standing up, before the day has started. Bougatsa is pastry, filled with custard or cheese or greens. Loukoumades are honey doughnuts. Pita gyros and souvlaki are the cheap lunch everyone actually recommends. Four different foods, eaten at four different hours, for four different reasons.
Blur them into Athenian street food and you have learned a phrase rather than a city.
Serifos: the seasoning is the tell
The Serifos case is the one this companion has already made at length — cheese matured underground, cumin in the louza, three separate words for fennel — so it is not made twice here.
What it contributes to this argument is the shape of the answer. Serifos versions of louza are documented with cumin. Not only Serifos uses cumin, and nobody has established that the seasoning sets these apart from every other Cycladic louza. The local thing was never the cured pork. It was a spice, and you find out within one slice.
Sifnos: the day, not the island
Revithada is the interesting case precisely because it is not Sifnian. Serifos has it. Most of the Cyclades have it. What belongs to Sifnos is not the dish but its week.
Prepared on Saturday. Cooked overnight in a wood oven that has been fired and then sealed. Eaten on Sunday.
The chickpeas are ordinary. The calendar is not. And a food tied to a day is tied more tightly than one tied to a coastline, because a day comes back every week and a border does not.
Mastelo is the same trick in one word doing two jobs: a clay vessel, and the festive lamb cooked inside it. A feast dish, though — not a Tuesday.
Milos: the method underneath
Pitarakia are small fried cheese pies, which is the stronger reading of a name that gets used loosely. Koufeto is pumpkin, honey and almonds, made for weddings — tied to an occasion rather than to a place, which is its own kind of local.
And beltes is tomato, reduced and preserved. Less a dish than the method underneath a good many others. That is the smallest and most durable kind of belonging there is: not something you order, but something already inside what you ordered.
The question that works
Not is this from here?, which gets you a Cycladic dish described as a local one by someone who is not lying.
Ask instead what a thing is tied to. A morning cart. A Sunday. A wedding. A pot. The answers are specific, they are small, and they are the part worth carrying home.
Nothing named here is exclusive to anywhere. Not one item on the list. That is the finding, not a disclaimer attached to it.