How? I'm pretty sure the commentators have said there's no mechanism to do that, exactly in Han Dong's case.

There is a room with a large-ish group of people in it. Someone in it has won a lottery. How many people in the room have winning lottery tickets, if you had to estimate?

An MP being a spy is more likely than winning a lottery, but I still think it's fair to say the vast majority aren't. To the point where if it's not zero one seems most likely.

Edit: Even if my conclusion turns out to be wrong, I stand by this logic. Vote me down all you want.