Never mind, randomly triggered this time, not sure I picked anything different.
So if I remember correctly, scene 4 only gets called if you choose option 2, and then option 1 in the text conversation. Alternatively, you can also get it by choosing option 2, then option 2 again, and then deciding not to bring up the texts when you're talking to Cassie later. If you're not flirty in any way (I.E. you choose option 1 in the first choice in the texts) then Cassie will just say goodnight, and the night will end without any scenes.
Hopefully that explains why it wasn't triggering. It's hard for me to say without knowing exactly what you did.
Since I plan to do quite a lot of this conditional branching stuff, I think I'll probably make a walkthrough of some sort after the next public release.
As for why it's telling you you've been flirty when you haven't (Presumably just choosing option 1), It's because it works out what to tell you based on what scenes are unlocked. So if you unlocked the flirty scene, and then on the next run didn't unlock any scene, it just thinks you've been flirty again. I kinda forgot it was possible to actually not get any scene after already unlocking one of the scenes)
Circled, your scenario (I think)
Either way, what it says at the end is just flavor text really, and it'll be removed when the next version is released.