Actually the claims Ubiqiti are making relate to the news article Krebs wrote After everyone knew that Krebs used the criminal as his source. For some reason, Krebs chose not to disclose this in his follow up article. That’s the defamation. Krebs knowingly posted false information not in the original article, but in the follow up.
Reading the article of December 2nd it seems accurate to me. Ubiquiti was wrong about the scope, that the incident was external. It says the suspect was pretending to be a whistleblower. It sounds to me like the suspect wasn't a liar when whistleblowing so what would Krebs retract?
They would have to prove that he was malicious in writing the article and since it's his job to write articles about security, they're going to have a real hard time doing that.