This is not how any leader should behave. It's a childish passive aggressive bullying power move by the most powerful person at a company. It's disrespectful to that employee by the person at the top of the ladder. That sends waves of signals to everyone else and that alone to me would be a reason for DHH to resign because how are employees supposed to work respectfully with each other if their leader is so openly disrespecting another employee who is in a huge power imbalance to him.
That's extremely poor behaviour to say the least.
Having read the letter they reported it's clear the employee is fucking nuts.