The logical rule that you quote is perfectly fine: If it is true that (if A then B), and it is true that (not B), then it is true that (not A). If it were true that bad food would always lead to complaints, and there were no complaints, then it would absolutely be true that the food must be good. No fallacy here.
There are two problems. First, the statement that there are no complaints might be made up, a lie. The restaurant owners seem to be in denial here. Just because the restaurant owners claim there are no complaints doesn't mean that is the truth. If a lot of food is returned then I somehow doubt that there are no complaints.
Second, it is not true that there will always be complaints when the food is bad. It is a very cultural thing. In some cultures, people will complain, either because they like complaining, or because they want to give the restaurant a chance to improve. In other cultures, this doesn't happen. People assume that it is impolite to complain. They just don't come back. You don't get complaints, you just get an empty restaurant. Depending on the attitude of the restaurant owner, they can easily stop people from complaining. Which is worse for business than customers complaining.
Summary: You can have perfectly logical reasoning applied to false premises. If the premises are false, then the conclusion is worthless. A "fallacy" is usually applying incorrect logic to a valid premise and getting to a wrong or unproven conclusion. Applying correct logic to invalid premises is usually not called a fallacy.
(You could argue the informal fallacy of taking the restaurant owner's word for it when they claim there are no complaints; that would be "appeal to authority" since the restaurant owner should be the authority on that subject).