Trump stated his plan to lower food cost was to lower the cost of the energy inputs that he says are driving up the food costs; lower diesel cost for farmers and transportation and lower energy cost for fertilizer production.

If this will work or not, no idea. But it did play as a better soundbite than "I will hold the grocery stores who are price gouging you accountable for it" because that soundbite says "We have been letting them get away with charging you for 3 years and now that we have an election to win we promise to do something about it".