I'm a bit surprised at how Takagi clearly has all of you fooled.
More than 100 chapters ago (see chapter 28), she already invited herself into his bedroom when his parents weren't home, with results matching Nishikata's expectations far closer than anyone here would predict.
That incident clearly happens after this chapter (unless it was before Nishikata family decided to install locks -- perhaps they noticed some creepy girl sneaking into their house spying on what their son was reading or watching on TV)... so maybe Nishikata understands Takagi a bit more than people give him credit for?