You are neglecting chronological order in your argument. What you wrote doesn't happen until EP2 after the cum petition. The MC wants to know from Maya why she did it, and Maya says she can't talk about it. Why did Quinn say to Maya that she can't talk about it. The MC felt it himself that he was knocked out by a shocker? Oops. But he doesn't know that Quinn used that shocker. Even we as players don't find out until Maya tells the MC. This gives the MC the opportunity to warn Maya about Quinn, and Maya suggests herself, so maybe she can talk to Sage.
I imagine Quinn has known the MC for a long time, because in EP1 there is a scene of Quinn and Riona where you can tell by the look on Quinn's face that she just recognized the MC. Riona looks at the MC with some skepticism, but Quinn has a slightly astonished look on her face. Quinn is also cautious because she may know the MC and therefore knows so that the MC follows rules.
The scene you describe is important in that Quinn realizes that the MC has evolved in personality and thus has probably become more interesting to Quinn. It's only after that that the guitar is stolen by the MC. But when he gets his stuff back, there is a strong indication that Quinn knows the MC from before. She asks the MC if he has sex often. All 3 answers to this confirm one thing. That he doesn't have sex often. If the MC answers yes, Quinn doesn't believe him. If he answers no, Quinn says she didn't think he would be so honest. If the MC gives the third answer to the effect that it's none of Quinn's business, she says no to that. Does Quinn know the MC's sexual resume? Even we as players didn't know him fully before the interlude. As a result, Quinn offers the restaurant to the MC. The picture afterwards of Quinn is also good. She looks after the MC while clenching her fist. She's going to fight for the MC.
Quinn is definitely an interesting/fascinating character and sexy. Still, each player must decide for themselves whether or not the MC should approach Quinn.