The article says that it’s six gigahertz and that they are putting one unit on each side of the wall they want to blast through. So the signal is extremely strong right at the wall and then goes through it weakening and hits the other device and then is re-transmitted or whatever. By putting the routers directly on the wall, next to each other, they have enough power to get through the obstruction. But if they were in the middle of the room, for example, they probably would not.
Source: A passion for wireless technologies and myself being a licensed amateur radio operator.