
My bad, but it is quite confusing though.
Though, the guys in the first chapter were figuring out why Hyesung is not posted on Jungwon's profile. Didn't think they were body shaming per se, they were just discussing (though they were rude about it) what the reason might be.
And the whole body image in this case is less about the generation but culture, both Korean and fashion industry culture.

I understand that they didn't say it to his face, but people have no business commenting on someone's body even if the person is bot present
That does more harm than good
As a person who's been through all that to the point where it left me bedridden and sick for YEARS I can guarantee that commenting on people's appearance and/or flaws is never a good idea unless that person's asking for it
And I agree with you that culture has a lot to do with it, but I specifically said younger generations because of the social media
Just look at some of them talking, they're calling everyone fat
You cannot fit their standards unless you're drained of every last gram of fat in your body
Body shaming was always a thing, but it's getting worse and worse because of the social media
And social media is mostly surrounded by younger influencers
Aaaand that's what body shaming does to people
The guy is suffering, even he himself said that his legs are shaking, yet he was excited about the fact that he had endured all the pain even though he was perfectly healthy and athletic.
It's so heartbreaking