I feel like he did lead him on though. At the very least, his intentions towards Joon were insincere and shallow at best, which is very rude towards someone who is sincere. Yoon should have taken Joon into consideration throughout all this. I do get that he is confused, but I don't think that excuses Yoon from not factoring in the fact that Joon did have feelings for him and could therefore be misled by his actions. And I 100% agree about Joon. I was pleasantly surprised when Joon decided to get clarification immediately. It's so rare to see that even in the real world.
Your right. Yoons intention were horrible and I'm not so keen about them either. And he has to take responsibility for hurting (or leading him on, that does fit I jjst realised) Joon on.
I don't think Yoonseol led Kang Joon on. He's developing feelings and had to make a choice (continue their relationship or not bc Kang Joon overheard them) when he wasn't ready to. He knows he probably has feelings for Joonie but they aren't that deep yet.
That doesn't change the fact that he's hurting Kang Joon and that he ended their relationship so I'm interested how the author is gonna make them get together again.
I also like how there's no unnecessary miscommunication and how Kang Joon immediately wanted to clear things up. Probs to him.