I have not received those threats myself.
What I've heard from other people, including the person I spoke about, is that those threats are like this: They would follow their family, their extended family or whatever. They would take pictures of them, send them to them and tell them to return. Their objective is to get them to return to China or wherever their homeland is. They take pictures of their extended family and send them to them in a way that is threatening them to return.
I think most of the time they're saying that if you don't do this, this and this, then something will happen to your family.