This was a Silicon Valley venture capitalist publicly complaining about Tesla, not a random blogger. So there is almost certainly a different social dynamic at play that we are missing.
Silicon Valley is a relatively small world; venture capital is even smaller and more incestuous. While most people here have not heard of Stewart Alsop, Elon Musk almost certainly knew of him, even if they've never met. Elon Musk may have been insulted because venture capitalists in SV are generally not expected to so openly criticize other SV companies (especially those funded by rivals?), and when they do criticize companies, they certainly don't insult founders. You can't deny that "you should be ashamed of yourself" is insulting to Elon.
You should be ashamed of yourself is an insult specially if you are writing a public letter to Elon Musk.
It was meant to be insulting had he written just a normal blog post on a badly managed Tesla event he would not have gotten such a response. If you are going to insult him publicly Elon can say fuck off in public or he can show you how to fuck off. He chose the more picking reply.
This open letter bullshit is annoying write a blog post or article on something but don't post open letters if you don't want a reaction good or bad.
Course you can deny that. It is nowhere near an insult to call someone out on the behavior described in the article, and to tell someone he ought to feel ashamed is also not an insult.
You are missing the human aspect. An insult can be true but still insulting. If a random person calls me on the phone and tells me that I was incredibly lazy this weekend and I'm just a lazy, lazy person on the weekends, that would be true, but it would also be insulting.
And that's exactly not what was happening here. It was not a random person, it was not about off-time, and it was not a generalization of specific behaviour, but targeted critic of a specific occurrence happening to the author (or in your example, the caller).
But by the way: If someone tells you you are lazy on the weekends and you actually know you are lazy on the weekends, that is also not an insult. It is just a true observation. If you feel ashamed then it is because you don't want to be lazy on the weekend, for whatever reason.
It is possible you mean that as feeling insulted by being judged. But that is another story and not the definition of insult. Insult would be if the caller would call you a lazy piece of shit for being incredibly lazy on the weekend – the explicit defamatory judgment. This honor insulting part is missing from the original scenario.
Silicon Valley is a relatively small world; venture capital is even smaller and more incestuous. While most people here have not heard of Stewart Alsop, Elon Musk almost certainly knew of him, even if they've never met. Elon Musk may have been insulted because venture capitalists in SV are generally not expected to so openly criticize other SV companies (especially those funded by rivals?), and when they do criticize companies, they certainly don't insult founders. You can't deny that "you should be ashamed of yourself" is insulting to Elon.