Yes, they come from China. However, they are handmade. As Galen noted, the "handblown" terminology is a common misnomer for handmade marbles. I've seen it used for years (in old newspapers and such).
If I were trying to sell them, I'd describe them differently, but I'm not trying to sell them. So .... well, I'm out of anything else to say. But they are indeed handmade to the best of my knowledge.