Samuel declares that the people of Zarahemla “do cast out the prophets, and do mock them … even as they did of old time.” Perhaps Samuel reference events that have not been recorded. Perhaps he meant the treatment of Abinadi. However, it is also possible that he referred to the Nephite origin story of those in Jerusalem threatening the prophets, and Lehi, the father of the nation. That would make sense of what Samuel suggests that the people say to themselves: “If our days had been in the days of our fathers of old, we would not have slain the prophets.” That suggests that it is a story of the origins, and the people suggesting that they are better than those who would have slain the founding father. It was a story they had to have known.
What Samuel declares is that even as they think they would not have persecuted the prophets of old, they have actually cast out a real prophet that has come among them. Samuel had been turned away once, and the people had witnessed Nephi prophesy, and yet still fell back into their unbelief.