not at first. he figured it out replaying the night in his head the next morning.
Reread the previous chapter, he figures it out in the morning when he has very vivid flashbacks of his night.
At the club he can't remember or see who he's talking to and that's why the uke says do you even realize who you're sleeping with because he looks like he doesn't know
The reaction was underwhelmed tbh I'm still doubting he figured it out
Wait you might be right, Cinderella might be slow af
he realized it that night. the part after cheol asked about "who trained you like this" (something along those lines), he replied "that's not case. you never strangled me, cheol-ah". that was when cheol snapped back to reality and realized he was having sex with minyoung. maybe it was a purposeful translation choice by the translator when they chose to make minyoung's response be in third person. i'm not fluent in korean or anything but in the raws, during that part, minyoung was using the pronoun "you" instead of using addressing cheol as a third party "he".
side note, minyoung always refer to cheol as "cheol-ah" which is could just be because cheol is younger than him or he does it as a form of affection (⌒▽⌒)
I'm so confused so he knew it was the uke?