Because it is hyperbole.
Will this affect US wheat prices?
Yes, because they are priced on the global market.
Will it mean citizens of the US will not have enough wheat to eat?
No, generally it won't, because the US doesn't import wheat at all.
https://www.wusa9.com/article/news/verify/the-russian-invasi...
Pay attention to the articles, many of them confuse global supply with exports, as if all countries need to import everything they consume. That's not true. These fluctuations will affect people and prices but the reporting is often hyperbolic and incorrect.