It was illustrating narcissistic personality disorder. Debating whether or not Musk delivers, or what personality traits might be behind delivering or not, is irrelevant to whether or not Musk illustrates NPD. It is easy to find examples of his behavior that matches [a layman's understanding of] NPD, so it seems fair.
Saying that Musk's personality resembles NPD doesn't say whether he is or is not effective at some tasks.