true, but here it's the context that matters, In-Hun meant it as an insult and to make him feel cheap and worthless.
I guess it's more like people were angry because In Hun was being hypocritical and was making it as if it was Nakyum's fault that he's in his predicament to begin with. The sad thing is Nakyum would probably believe him. :( Poor baobei.
I think a review I saw above explained it perfectly:
"That piece of shxt knew that Nakyum was being forced into doing things he didn't want to do. Told Nakyum to go back when the boy tried to run away. And now he turns around and makes it sound like it was okay for Nakyum to go through all that for his sake even if he didn't enjoy it. Yet now that he does enjoy it and doesn't just roll over to pant after him like he used to, he wants to act like the sexual acts are now depraved. But they weren't before, when he needed something???"
Okay so he called him a prostitute... I get why people are mad but its not really an insult prostitution is a job like any other.
Although I get that back then it was a massive insult but still being mad about him calling the painter a prostitute is meh compared with the fact he has done worse by manipulating the painter and making him feel guilt for being gay and having been raped.