Completely believable to me and a very astute set of observations.

I've been there. I know exactly the difference you describe between justifiable fear (the unknown physical consequences of diving off a board for the first time) vs. the far more powerful irrational fears (mind reading that everybody is looking at you and laughing at how awkward you appear, especially the cute girl over there that you are quite attracted to, and how disappointed she's going to be if you mess up the dive; maximising the importance of your dive performance in your mind because you believe she wants somebody perfect, whereas for all you know she thinks it's cute, etc.).

I especially enjoyed your conclusion - it's one I reached before, myself. Socially awkward people who eventually develop out of their behaviour have a great gift - they can recognize and empathize with other socially awkward people far better than the natural extroverts and, through their words of encouragement and empathy, share the gift of self-confidence.

Reality is stranger than fiction. I didn't find the story unbelievable--I'm far more conservative on trusting the psychoanalysis than the events--perhaps I've just had exposure to more "weird people" than the above commenter. If you had written the kid had let out a shrill scream of rage I wouldn't think you were lying from that alone, people are weird and have weird reactions to seemingly trivial things. What never ceases to amuse me is the array of reactions others have when meeting (relatively) famous people they are fans of.