Hmm I think he did not forget him. It just so happens that he misnamed chaejun as junhee and he forgot his face because they were just 9 and 10yrs old back then so a lot of time has passed and also chaejun evolved as a giant
I'm thinking he just didn't put two and two together. I mean, he was what, 12 back then? and met chaejun again 10 years later.how well do you remember the faces of people you only knew as a child, never had to think about again in 10 years, never had a photo or anything? and sure, you met someone woth the same name, but how rare a name is chaejun? and he doesn't remember him either, and he has a completely different vibe from the kid you were friends with 10 years ago, whom you though was A LOT younger than you, not just 1 year.
as a kid he never met the uncle either, and maybe when the uncle decided to falsely accuse him of giving his lover trauma, maybe he just said that chaejun was intentionally locked into a room for days by him, you know, not mentioning about the construction site.
also chaejun never talked about the incident himself, so no clues from there, and he didn't think something bad happened to little chaejun back then, so why would his mond go there?
idk, to me it's plausible, especially considering how emotionally exhausted his family kept seunghyun
yoooo, i thought it was the older bro that misheard or misremembered the name when seunghyun said it and just acted all high and mighty and said no way I'm in the wrong, seunghyun must've been the one saying your name wrong
wait no, he was 9 or 10, my bad, even younger!
Now I’m just wondering how seunghyun also forgot everything