There were different chat groups for different people in this family. For instance, there was a family group where everyone was added regardless of their age. There was one with only the young age. Well, men had their secret chat groups while the ladies had their own.
Just like Xiu, Nora and Dylan had their separate group chat where one could find all kinds of bickering, bantering, and nonsense. That chat group was a film on its own.
But currently, Cali's blunder was that she sent the text in the friends' group where everyone from the younger generation saw it including Darren. While Xiu was the only one who replied and the rest chose to keep a mutual stance to being silent in this matter. It's not like there was anyone unaware of the complications between Darren and his birth mother.
Cali didn't want to tell this to Darren but she wanted to give a heads-up to Xiu instead. Who knew she was so lost in her head that she made such a mistake?