Why this tiny Italian restaurant gives a discount for bad Yelp reviews

It's good to see someone standing up to Yelp's questionable ways in which it runs its site. It's ironic that Yelp tries to extort businesses into giving away free food and drink, as well as paying for advertisements and placement on the site, but a company offering discounts for one star Yelp reviews is in breach?

I am coming over to the states in a couple of weeks and will make it my mission to go to this place and give them my business because I respect what they are doing.

I don't see how they can be in breach of yelp's "terms of service" seeing as how yelp is also taking the stance that restaurants will be listed whether they want to or not