im not sure if this is a correct answer to ur question but more of a thought in response, i think it was possible for yeon (the black haired seme) to touch the red string as a child in the dynasty lifetime because of the specific circumstances. When he went back to the village and stepped inside the storage room to read the note (i forgot the specific chap sry!!) it said that it was possible under certain circumstances where the waters are calm and the rock is sleeping or something like that. also it may have been because the string wasn’t actually on the person (kihoon) itself yet, but still on the rock?
Ooh right², thank you for telling me about that chapter! And yea, if his string was tied indeed to a rock, was there another chapter that Yeon tied his string as well to blonde guy? (I vaguely remember if there was a chapter of that incident and which specific chapter).
Basically, blonde is a Blazing Flame Soul (so he doesn't need or wasn't supposed to have a fated pair in the first place). However due to the timeline of the past wherein the young master (black-haired seme) tied his red string to the rock, (unknowingly or knowingly that the blonde is there by or behind the rock), the present time became what it is now (the First Season of this story) — blonde's encountered misfortunes after misfortunes despite being a buffy ball of sunshine and a magnet for supposed luck.
One question in mind that I've thought; how is it possible that the black-haired seme was able to touch and tie his string to the rock? Normally you couldn't see nor touch your red string unless there's something going on (to which it'll be found out in the story of season 2, hopefully).
Sideline questions, when will be the release for season 2? Would like to know the date if they've posted, thanks! And then, what will happen to them in season 2? The shiver in me's getting a bad feeling for whatever's in the past.