Gosh, I really hope this was sarcasm but after someone posted here that Siwon is not dumb, just 'pretending' to be dumb to catch the Chinese guy, (my favorite one, honestly) I don't doubt anymore that readers will come up with anything trying to explain the character....
That's probably the best way to understand the story.
ha, omfg it's so true though. If the author did clearly state that Siwon had a learning difficulty it would make readers maybe sympathise with him and understand his bullshit. I don't think he has health problems though, Siwon is just a pain in the backside, as Jinha said in an early chapter, Siwon chooses to see things in a way that makes Siwon look good and everyone else look bad.
I think this author should be commended for creating a story about a mentally challenged character. It's the adventures of an uke who has a learning disability and the guy who loves him very much and must protect him from others and from himself.
Siwon is a very sweet boy trying to live in a world of adults and trying to handle situations far beyond his mental capacity. What we all take for granted, it's not so simple for him. He can't make the connection between what he knows and what he should expect, correlation, behavior pattern or red flags for instance. That's why what would be very simple and basic for a child, like don't go drinking with someone who already drugged and sexually abused you --- such simple notions are really hard for him to understand. All this problems with Lu Xuan could have been easily avoided if only he had listened to Jinha for instance or even if he chose not to, plenty of proof was given for him to make his own decision but his judgment is of a small child who gets distracted by the promise of a candy and accepts the offer to get in the car of man everyone warned him about. Thankfully he has friends and people who love him and will always be there to save him. Jinha must love him very much because it's not easy to be responsible for someone who can't look after themselves and will always need to be rescued.
Still, congrats to the author for the courage to create a love story between a mentally challenged young man and the man who will always forgive and be there for him every time he needs it.