The way of eating natto that is depicted here is the standard method when the natto is eaten together with white rice. But there has never been a method of eating natto that is universally acknowledged as the one "correct" way.
Throughout its long history, natto has continued to evolve in different ways according to the region and the historical period. To take just the example of seasonings, natto has been enjoyed with shoyu as well as with vinegar, olive oil, sesame oil and so on.
We encourage you to find your own favorite way to eat natto.