OK so they have made an off the cuff calculation of how long it would take to orbit the Sun, if in fact planet 9 is really there. Who knows, but it's still fascinating.
If it is a captured planet, which system is it captured from ? How far away is the nearest solar system ? I can understand captured moons within our solar system , or comets/asteroids being flung out of orbit. Even planets being flung out of solar systems. But they just lurk out in interstellar space, it's a very long way from here to anywhere out there.