i absolutely LOVED that twist at the end of episode 4! aside from it making me curious about the next ep and whatnot, i love the trope subversion. you have giseop calling jinwoo who isn't picking up his phone. giseop sees him talking intimately with a girl outside as the automated voice in ear is saying "the number you've dialed is not available." then we see a shocked expression and the dinner giseop bought to share with jinwoo is dramatically dropped on the ground. we all know what that means - surprise and instant jelaousy, heartbreak, what may follow is only a dramatic "jinwoo, what are you doing??"

but nope. cause first, that's not what's happening and second, because that can't happen. because that's not who giseop is. he would not jump to a negative conclusion the way jinwoo instantly would even if the conclusion is the truth (jinwoo IS on a date. what he said to hyejin, though, remains to be revealed and i believe he turned her down in some way or another). had hyejin not been someone giseop deemed dangerous and had his attention not been a hundred percent on jinwoo's safety, he might've been surprised but his reaction would have been much more tame, probably to a degree that would annoy jinwoo (who, i'm fairly certain, would fall for a clear and loud display of affection such as a jealousy fit - being dragged away for safety rather than out of jealousy is a pretty solid move too, though)

point is, even before we realise giseop knows hyejin and we see he's running towards jinwoo with a concerned expression on his face, we should know something is up by the simple fact he would not react like a typical jealous love interest.