There tend to be three kinds of kingmaking: revenge, social dynamics, and wanting to leave. All of them have something in common: they are done for reasons outside the gamespace. They're violating the boundaries of the game.
Revenge (what you did) is out-of-bounds because it's using the game to win future games rather than playing the current one.
Social dynamics and wanting to leave are out-of-bounds because they're using the game for rewards that have nothing to do with the game.