Some crucial context for that piece of news: https://worldpopulationreview.com/country-rankings/food-self-sufficiency-rate-by-country

Japan ranks 6th in the world for food self sufficiency - pointing at this being a nothingburger. At the same time, if you look at the land area needed for self sufficiency the picture gets quite different, sending Japan way down at 157.81% needed for that. So it could be an extortion scheme on the part of the USA.