Musk is one of the most impressive entrepreneurs of our time. But he is also just human. Sometimes "totally fucked up" as you put it is the way we react, even when we shouldn't.
Musk could have chosen to ignore calls for help, but instead he exposed himself to the risk of failure. Then he was told his efforts were just PR and to "stick the submarine up where it hurts" by one of the now famous divers who currently speaks from a position not much less public than Musk's. Being told he had ulterior motives after repeatedly asking the person in charge of the rescue mission if they were sure they wanted his help (as the email shows), and after spending what is likely hundreds of thousands of dollars and days trying to help, is extremely disrespectful. I agree that he should have ignored it or simply rebuked it. But I understand he couldn't.
Can you imagine a response that doesn’t involve libel? How many people did Mark Zuckerberg call out as being pedos after his $100M attempt to save New Jersey schools flopped?
Even if insulted (and how insulting were these previous comments, really?) a random diver speaks for himself, a public figure heading and representing multiple big corporations should be able to keep his mouth shut instead.
He simply told Musk to go away and take his toys with him, before he hurt someone. Was he direct and a little bit rude? Sure, but the overall situation was quite tense, so there wasn't a lot of time for fine detail and detailed explanations.
It's understandable to be pissed off and call the other guy an asshole. This is totally fucked up and not at all understandable.