This message's purpose is to educate customers that the legal threats businesses are making in those situations are idle ones. They're idle ones because of the first amendment.
It's perfectly relevant here.
Yelp's message should be about libel and slander and things like that.
http://thescoopblog.dallasnews.com/2016/06/plano-couple-hit-...
The business sued for libel. The customer's lawyer filed a motion to dismiss, citing first amendment rights. The business dropped its suit. Nobody's laughing.
The business filed a second suit, this time alleging the customer violated a non-disparagement clause in a contract with the business. The customer's lawyer filed another motion to dismiss, citing their first amendment rights. That one's still pending, but nobody's laughing.
Here's a copy of the ANTI-SLAPP motion to dismiss the second suit. SLAPP laws exist to ensure the courts are never used to impede your first amendment rights via the cost of mounting a legal defense. Showing that the defendant was exercising their right of free speech is a required element of making that motion, so it's certainly not going to provoke any laughter in the courtroom.
http://www.citizen.org/documents/DuchouquetteSLAPPmotion.pdf