Ik it's literally been months since this was posted, but I've re-read this chapter a couple times and still didn't understand a good bit about what was going on. Though after reading this scene in the web novel, it's a lot clearer to what is going on. None of what follows are spoilers since they are all revealed in the chapters of the web novel that correlate with this chapter of the manhwa.
So, basically.
- Vinter knows that he's talking to Penelope Eckart here and specifically threatens her in this scene rather than "a certain client" (the language was confusing)
- The reason Vinter went after Penelope in normal mode is because she went through this same series of events (requesting an informant, meeting the kids, conversing with a masked Vinter) but ended up blabing about Vinter's students/the sorcery despite his warning
- Vinter's interest actually goes up twice in this scene; once, up to 8%, after Penelope replies "I'll make sure to keep my mouth shut, then" after Vinter's threat (no depicted in manhwa) and then after she tells Vinter to deliver the handkerchief with the message "Reciprocate" which I think is where he realizes that she's the woman he met at the ball? I'm not 100% about this part still since he already knows it's Penelope Eckart who made the request thought somehow doesn't know that Penelope Eckart is the one he met at the ball. Idk
- Also, I saw this in the comments but the reason Penelope chose to look at the choices/ choose a choice that seems to threaten Vinter is to figure out if this event occurred in the actual video game and why Vinter ended up assisting the heroine and bringing down Penelope, resulting in the conclusions in the second bullet point
BTW, this chapter of the manhwa correlates to chapter 34/35 of the web novel if you want to read this scene for yourself
Hope this helps!