Mmm, I've been wondering about this for a while seeing how the chapters unfolded. I was pretty convinced that Saki did kissed Kanon at the fireworks event, but was also clear that she wasn't expecting Kanon to return it (cue Akira's "it's not like the right kind of love has to be one that is fulfilled"). She only asked that Kanon continue on being friends (watch the fireworks together next year). I had interpreted the bonus bit then, indicated that something did happened which Kanon was telling herself to act normally.
At this point, Saki pretty much accepted and acknowledged her own feelings towards Kanon. Now we're seeing the perspective shifted from Kanon's view. And...we sort of can see how Kanon can be pretty bad at picking up people's feelings, and Rinne even tried to hint it to her. Rinne knowing her own sister, probably also figured that it's best Kanon figure it out herself.