I'm under the speculation of him taking off after the repair then fallen causing him to crash land and then letting himself be captured in the absence of a present Kell to declare himself Kell. Though this is all from foil hats, I'd love to see mom (Mara Sov) come back as the ruler of the fallen as a whole since most houses are now gone. I feel one of the two will be Kell or at least unite with fallen in the next dlc.