The early Solar System was a turbulent and chaotic place with icy material hurled far from the Sun, becoming the Oort Cloud. Larger objects and planets were probably hurled into the Oort Cloud too, and some might have been kicked out of the Solar System entirely. If a similar situation happened in other star systems, planets could lurk out in the Oort Cloud.
I think disagreement about the planet status of Pluto may be what’s behind the different names.