I certainly feel that Joohee might be delussional, because, from what we have seen... Hyunsoo had other messages with other girls in his phone, too... Sure, might be some of those "let's exchange numbers cause I found you cute! <3" kind of thing... but if the dude was disinterested, he would have simply... not gave them his number, I guess? Or blocked them... which he certainly didn't do.
I feel quite bad when someone like Joojee (character or not) do this kind of thing (being the moving seat thing... or the "talk"), as if they are in their right to do so :/. Or maybe I'm projecting myself a bit... That kind of stuff hurt a lot no matter if it's in "good" or bad faith.