Xiao Keke and the others didn't know that Mu Lianmiao and K were not related by blood.
Nevertheless, what Xiao Keke had always known is that Mu Lianmiao liked Musheng very much. She thought their affection was harmless, but in Xiao Keke's heart, she was convinced that their relationship transcended love.
Now, suddenly knowing that Mu Lianmiao was in a relationship with Musheng, who was supposed to have no connection with her in a million years, to Xiao Keke, this was tantamount to thinking that Mu Lianmiao was simply too devastated by K's death, and since Musheng resembled K and was her disciple, Musheng might have taken advantage of her vulnerability...
No!
Musheng isn't that kind of person, how could she think so?