what would he be manipulating exactly. all of the chapter we’ve gotten from his pov track with literally everything he’s said to jinwoo. it’s so clear that the “what if im not the person you think i am” relates to the backstory he’s telling jinwoo ie “what if im not as strong/untiuchable/great as you think i am” bc of his family dynamic
That said, if the twist is that he is manipulative, it isn't something that will be made clear to us readers just yet. I’m not saying there isn’t a chance you’re right, there is a certain logic to it, but his family background could just as easily have turned him into a negative, manipulative person; he might feel suppressed and believe that this is the only way he can assert herself.

Foreshadowing? Chapter 43 Page 6.
“What If I’m not the person you think I am?”
Manipulation?