Heinz ketchup company uses tomatoes, which are grown on U.S. soil and is completely homegrown. It does not import tomatoes from Mexico.
According to an NPR report, Ross Siragusa, the head of global agriculture for Kraft Heinz, said that a sun-baked field near Los Banos, California, will produce about 60 tons of tomatoes in each acre. A mechanical harvester collects a stream of bright red tomatoes and put them into a big truck driving alongside. Within a day, a processing plant in Los Banos will turn these tomatoes into a paste. Weeks or even months later, the paste will become the central ingredient in ketchup.
Heinz Ketchup's company website claims that all the tomatoes used in their ketchup sold in the U.S. are homegrown. There are no further pieces of evidence to show that the company imports tomatoes from Mexico or elsewhere. Thus, we can say that the claims regarding Californian tomatoes being exported to foreign countries and then imported back to the U.S. are baseless.