On the one hand, I don’t know that it’s fair to sue a company over your poor understanding of technology, or user error. On the other hand, if he worked for DARPA and was using imessage to talk to his boss or his team about a project that was then leaked or sold by someone living in his home who had access to his home laptop because he didn’t know that the messages he deleted weren’t deleted in real time, and he was fired from his job, that seems like something the company should make very clear when deleting the messages in the first place. A simple warning “Delete this message? Please be aware that deletion is not instantaneously across devices.” Would do.
Incognito mode actually has to tell users that it doesn’t prevent your ISP from seeing what you Google or what websites you visit while using it. They literally had to add a notification so people would know because people didn’t know.