Several things severely wrong with this example. The employee didn't talk to an outsider, they didn't talk to someone the CEO would be likely to have known personally, and they're so far removed from the CEO nobody thinks they'd know them on a personal level.

You just can't talk about a CEO as if they're a person interacting and hiring people individually because they just don't.

In a small company a CEO may approve all hiring. In a larger company they delegate that. But they run the company. Everyone in the company including those hiring reports directly or indirectly to them.

When an employee communicates broadly inside a company, even if it's not directly to outsiders, that is essentially public. As we can see in this thread some random person chimed in with the details. But s/neighbor/your wife/ if that helps the analogy and insider vs. outsider is the issue. It's an imperfect one as they all tend to be.

This is why for example quarterly results are not generally communicated to all insiders in a company before they are released, because they are going to leak.

I think my analogy, though imperfect, demonstrates that when you have some sort of employment or other relationship, "bad mouthing" the other party, either in public or in private, is expected to be damaging to this relationship. The CEO of your company is the closest thing to the single person employing you. He runs the entity that employs you.