He was being honest and I actually respect him more for putting a former employee that obviously was trying to get sympathy from the Reddit community, in his place.
He also publicly spoke out about someone's work ethic and performance of which we're only getting one side of the story anyway. If his real name is associated with his reddit profile then future employers will see the CEO of a public internet company lambasting him. Whether it's deserved or not at the time is irrelevant; there are plenty of people who, for one reason or another, do terrible at a job and later are highly valued. This could ruin any attempt at redemption.
I call it "thinking with your tattoos". People simply aren't cognizant that decisions and actions have long-term consequences. You may really want that tattoo on your face, but it will make you virtually unemployable for the rest of your life. They're simply unable to project out complex interactions of consequences, their brain simply can't do the calculus or views it as overstimulus or something simply filters out everything to do with long-term planning and executive function.
In the U.S. it does, since untruth is a required element of libel.
The employer would have to prove it's true in a suit hence my comment. Paper trails are king.