World Travelers, or "Foreigner", refers to people whom are reincarnated or came from another world.
In history, there were several cases whereby some people were either reincarnated, summoned, or came to this world by accident. In some cases, they were summoned here, hence the Summoned Ones. On the other hand, they could have arrived from another world by accident, or were simply reincarnated. There was not a fixed way of how the World Travelers came.
Being reincarnated tends to happen randomly, especially those whose souls with strong intentions engraved upon them. Although there are those among the reincarnated whom still remember their past life, to have reincarnated from a different world is exceedingly rare. Moreover, one would normally be reincarnated as a human. However, there are very few exceptional cases. For someone to be reincarnated a monster, and from magical energy itself, is something that remains unheard of.
As for those whom came to this plane by accident, it also happens randomly. However, unlike those whom undergo reincarnation and have to be reborn, they arrive here with their original bodies intact and whole. In addition, they still retain their original memories.
In any case, setting aside whether method they came by, it is a known fact that those whom came "naturally" will possess special intellect and acquire some unique skills, based on the characteristics of the individual themselves, naturally upon their arrival.
Existing records of reincarnated being renowned for their wisdom do remain, although there are most likely those that were never recognized.