Your edit involves a specific definition for a specific case of defamation suits.

I don't see how being a public figure means you don't have the right of protected speech.

But you know I'll bite; your link states that you can become a involuntary public figure, you don't seek it but you still are and you are considered as one for this case.

Let's say the teacher was picked up by a news crew and made into a public figure.

Can they be fired then?