Public Shaming Dine And Dashers

A group of adults dine and dashed 400.00 worth of food at a restaurant. The owner posted onto instagram to public shame them into paying their bill. It became viral through a different instagram page that owner has no control over. A random person advocating for the people who dine and dashed, paid the bill later. Now a random supposed “lawyer” wants to sue the restaurant for defamation. Is that possible in California? Any legal help or advice is appreciated. Thank you.