The guy told it like it was. It was a PR stunt and nothing more. His submarine was rigid and stood zero chance of navigating the intricate cave system, of which the caver was an expert. Elon didn’t like his sub (and him by extension) being ridiculed, so he used his social media clout to make an unsubstantiated and nigh libelous claim that the guy was a pedophile.
Whatever Elon’s retaliatory reasons are for his vindictiveness, a rational person can safely assume that those reasons are tied to his hollow soul and crêpe-paper-thin ego.