Clark's speech to Superman-X about a "loner" friend is a reference to Batman, and his reluctance to join the Justice League way back in the 21st Century.
Takron-Galtos, the Prison Planet, has appeared in several incarnation over the years of stories told in the Legion comic books. It is usually a separate world, unlike the satellite depicted in this chapter. At times it has even been shown as the former Earth, abandoned by humanity and converted into a penitentiary for the United Planets.