My working theory is:
Seunghyeon's brother "managed his friends" so when his brother came looking for him at the construction site (and he disapproved of chaejun) seunghyeo had chaejun hide and wait for him to come back, but his brother dragged him away. So chaejun wasn't trapped he was just waiting for seunghyeon but after that day neither family let them go to the construction site again which is what actually traumatized chaejun
Seunghyeon's brother "managed his friends" so when his brother came looking for him at the construction site (and he disapproved of chaejun) seunghyeo had chaejun hide and wait for him to come back, but his brother dragged him away. So chaejun wasn't trapped he was just waiting for seunghyeon but after that day neither family let them go to the construction site again which is what actually traumatized chaejun