I don't know what seems the be the method or reason how he was hacked but the reality is that we shouldn't really trust our own wallets neither if he got hacked. I mean think about it, dude is a bitcoin developer, he probably knows more about how safety works let alone just being safe, so he had all the knowledge and tools and items he needs to be safe and he still got hacked and all his money was stolen.

This shows that we can't be safe if we do not know what we are doing. The best thing we could do right now would be making sure that its on a place that is secure which is cold wallets and offline, that would be a lot better for sure.