Maybe it was all just a wildly lucky guess. Maybe aliens in time machines provided Joseph with that information. But we could honestly state that there were grounds for plausibility - the best we can hope for in dealing with the Book in purely intellectual terms. They sure do. It's quite exciting, really.
Every detail is plausible.
In fact, an ancient burial site in the proper, plausible location even carries essentially the same name - Nehem. So far, they always change the topic. But I can't blame them. This exercise can be carried out for other places and events, though the supporting evidence is often less dramatic than in the case of Bountiful and Nahom. For example, does a plausible candidate for the Hill Cumorah or the River Sidon exist.