If you say something about a person that you cannot prove, and that something can do harm to their character or reputation, you're liable for libel or slander.
And it wasn't just about wrestling an alligator, he also mentions, "Muzzillo liking Michael Jackson and having a 'gay old time'". That's definitely slander.
Also, if the teacher was willing to file charges, I'll bet the kid was an asshole in class. The teacher obviously didn't like him. If he was annoying in class, then I'm glad that the teacher was able to get revenge on him.