The more Kyran thought of it, the more he was convinced that they were really not originally from the Human plane— or at least, most of them.
One of the reasons he thought this, was that the Remnant Souls in the Misty Forest seemed to be waiting for Caelan's return after he left to confront Layla. They did not seem to have recently 'joined' Caelan's side as well, making Kyran believe Caelan won over the Remnant Souls from another plane, while Layla's undying army was mostly made up of the human souls who had died in the ongoing war.
While Kyran pondered these things, he continued to listen to Stella's story.
Stella continued to tell him how Caelan eventually won over the second invaders. When he did, the humans thought they could finally turn the tables against the third invaders by having Caelan asked their assistance. However, before any of the human representatives could even talk to Caelan, the second invaders' attack became more ruthless.