snickersnerds:

I was also thinking the same thing! I think he wanted to see if they were truly over each other because he still has lingering feelings for Yeonsu. I don't think he would completely overstep and ask her out knowing Choi Woong still likes Yeonsu but I do see him revealing his feelings at some point. 

I think CW knows he has feelings for YS, even before then.  And that CW would gladly share/give anything to him except YS. So again, he'd be the catalyst for bringing the leads together - then and now.