This entire story is pointless. What was the point of it all if K is Matthew? It's not a story about revenge, it's just a psychopath messing with people's lives. Zero point in showing the girl at the beginning, then.
They were probably making good money off of sponsors so they changed the story to this in order to keep the show going.
That being said, at least the actors are amazing and the plot is fast paced and entertaining at some points, when u don't get too annoyed that its going nowhere.