My understanding of that conversation is that "a non-participant killing a participant is why the participant's time is frozen" but not why it also affects Shiranui. After all, the chapter also made a point to explain that Yurako was also affected because of her Ayakashi.
Mao wasn't mentioned though, so maybe for him it's because of the Byouki inside him?
My understanding all this time is that Shiranui somehow stole it from Masago and that's why he keeps her body with him. Maybe it will be explained in the next few chapters.