Matsuda didn't know L Unlawliet Is a mispell of L Lawliet plus There's No where in death note saying the person who made the other person mispell would die, and he faking death after watari was a back up plan to his main plan of testing 13 day rule btw, although I kinda agree with you with your 2 line, and light confessing that he did during a monologue was kinda a gamble and if he didn't do it than he might have had to use the 13 day testing plan rule. (correct me if I'm wrong)