Okay so I skipped for it a bit in the raws so if you want a bit of a spoiler about it this is my theory about it
so if you have already read tgcf you would already be familiar with the they're immortal so technically it's not grooming troupe... But here it's deeply rooted in the story, so I think ryeongs memories are returning without him noticing as his memories were sealed when his master made him blind to lock them away and stuff. I can't remember exactly what but Jae did something that made the seal start to go away OR something happens in his ascendant years that makes the seal wear off until he presumably remembers everything and isn't blind anymore.
So TL DR basically he doesn't know this and doesn't know why he has an attraction towards a child he took care of. I'm assuming Ari had something for Jay who was 3 years old when they met because Ari suggested they eat pork and wine together and told him that if he took too long he would find another lover. This is all how I see it though
i think for grooming there has to be intent n clearly ryeong saw him as a child the whole time he was one but idk if he still counts as one or not. kinda conflicted tbh but this is honestly an all time fav n ill check up on it when theres another 30 chaps lmfao