Wait

Nah even in the novel it happened like that. And not everyone knows. Only those in the pado guild, gaeul, and hong ye seung know rn currently. For lee sa young at first he didnt know, he was obsessed abt finding j tho but more interaction eith j made him realise

They all always had lingering suspicions already cuz they've been digging for his info from the start. Every clue led to him but they got to clear evidence. Now that he plainly revealed his powers, they finally can stop guessing ig.