The example she uses is that of someone owing a grocer money for supplying them with potatoes. In such a case, the set of facts, e.g. that the customer asked for the potatoes, that the grocer supplied them with the potatoes, etc., does not necessarily entail that the customer owes the grocer money. After all, this could all have transpired on the set of a film as a bit of acting, in which case the customer would not "actually" owe anything.