Quit via Automated Reply
When you’re on vacation, the worst thing that could happen is your office trying to reach out to you. What you should do is deactivate your phone, don’t receive email notifications, and wait until you’ve gone back into the office to put out any fires. Or, if you’re like this person, just set up automated email responses.
This person decided to use automatic responses as a way to tell everyone they quit. “I am currently out of the office and don’t plan on returning.” If you want to reach out to them, too bad. You’ll have to hire someone else to do their work.