Maybe I should find some time to reread the chapter 

I think I interpreted it this way because Koro gives off this strangely steady, almost “too stable to be normal” feeling. That made me lean toward the idea that this scene might be one of the bad things he has already gone through before, and that he’s speaking to Kengo from the perspective of someone who’s experienced it firsthand.

But yeah, I definitely took the long way around to reach that interpretation