The author’s brain tends to short-circuit when writing novels.
In short, this is another product of one of those brain farts. And I think that if this novel were rated by the standards of American and European movies, it would get an R rating at the very least, so read with caution. If you don’t understand something, ask Baidu.
The novel is told mainly from an observer’s point of view, so readers can figure things out for themselves: Who do you think the murderer is? What was their motive?
Special warning: Don’t trust a single word you see.