It's not a "just-bought" onion. What grocery store sells an onion with an eight inch sprout coming out of it? At least in the U.S. such an onion would be unsellable, which is why I think they found this one in a bag somewhere and decided to plant it.
Are we looking at the same photos here? It's clearly not a green onion. It has a large round bulb on the bottom that's more than two inches wide. Green onions / scallions do not look like that. You can see that in the very image you just linked.
