The little child doesn't understand jokes imo. It definitely hurt him. Imagine being a kid and ur parents are joking about trading you for money. He was definitely unwanted. He is a child. Whatever came out his mouth is probably in a fit of defense and maybe some manipulation from his grandma. He said he doesn't mean that and knows how much they love him. He is a hormonal teen who has yet to understand his emotions and the consequences of them.
Thats the whole point of byuls outburst hello.. his point was that at one point hyeseung abandonned him like grandma did. Keep in mind hyeseung ran away so when grandma went back to the house he was alr gone. Shes still in the wrong for leaving him with that pos father but byuls whole point is hyeseung also left him and he still loves hin

i seriously don't understand this kind of narrative the author is pushing for byul's character... like he can be fucked up in ways like he kept being compared to his father when he was training to be an idol (which eventually led him to not debut bcs his voice was "just like your dad's" LIKE THAT'S VALID AND IT MAKES SENSE WHY HE'S AN ANGSTY GROWING TEEN!
why are they pushing for an "unwanted child" narrative when we all know very well that both his parents LOVEDDD HIM SO MUCH, HE GREW UP IN A LOVING HOUSEHOLD BRO CMON?!?! even that stupid flashback he overheard didn't make sense bcs it was them joking around abt the two's issue back then (without stating how byul abandoned them, even jokingly)