The EU has a system-wide concept of products (mostly but not exclusively foods) that are by definition produced in a set region, by a particular method etcetera called the Protected Designation of Origin. This is inspired by laws in some of its member states (most famously France's AOC laws which protect Champagne) but because it's a system rather than being stapled into the law for one specific product it makes it practical to use for less famous things where the heavy lifting of actual legislation would be too much to ask. If your town produces a peculiar furry hat, and then one day sales of the furry hats begin to drop off because it turns out somebody is making replicas in China and selling them under your town's name, applying for PDO is a relatively straight forwad way to fix that across the entire EU without trying to attract attention from legislators in two dozen countries.
Of course PDOs can be abused (e.g. arguably protection of Newcastle Brown Ale was pointless, its only producers were indeed in Newcastle, but when they decided to move they simply applied to discontinue the PDO status...) but overall it seems like having a framework makes more sense than only doing this as actual national legislation (a rule saying Vidalia onions are from Georgia only works because the US government enforces it, the part in Georgia state law has very little effect)
It's why you can buy "Swiss Cheese" from Wisconsin and Bourbon Whiskey from Orlando.
I didn't grow up in one of the counties that are considered under the bounds of the Vidalia area (although pretty close) but we grew the same onions. They tasted, smelled, and looked exactly the same. Were I to try to sell them as Vidalias I could have been sued, but we were growing them for personal consumption anyway.
That being said what he's doing is something that is hard to reproduce simply because Vidalia onions cannot be grown except in a certain geographic area. You can take the same onion and grow it elsewhere, it will taste exactly or very close to the same, you just cannot sell it as a Vidalia. I'm surprised that there aren't more of the boutique style shops for things like Vidalia onions, Georgia peaches, etc.
Source: born, raised, lived whole life in Ga within a farming family.