Isn’t strange that Nighsong didn’t fall in the Reach area of influence considering how close is to Highgarden!?

Yeah, it’s a bit strange sticking way out there on the western end of the Stormlands. My theory about this, which is not supported by the text at all, is that the Carons were formerly part of the Reach and/or the onetime Kingdom of the Marches, and joined the Stormlands following a political dispute with the Reach Marcher Lords like the Peakes, Tarlys, etc.