Can I be sued for libel?

A restaurant posts ads on craigslist often (and in the wrong section of the site) and I posted a critique of the place, and they e-mailed back stating they could sue me for libel. I'm I correct that this is just a bluff? If they did go through with it, in order to sue me they would need to prove what I said was false and prove that my message that was up for 2 minutes on craigslist made them lose business, right?