Plant: Wild or Not?

I discovered a plant in my street and a reader knew it's name: verbena bonariensis. The plant grew on its own in a small messy flowerbed but I have been noticing it everywhere as a garden plant. In fact it's probably the most fashionable plant of the season. However I have also discovered a few growing on a small untended plot overgrown with typical weedy species like primrose and blackberry, their distribution has the chaotic pattern of self-seeding. Wikipedia tells us that the purple top is native to South America and that it does spread with the wind. So what is the plant in my street? Is it wild (read escaped), planted or planted but forgotten by its gardener? Whatever the case: I am feeling all Gilbert White hot on the heels of a plant about to turn weed.