He was speaking in Iowa but maybe he thought he was in Illinois, where John Deere is located. Or it could be he knew he was in Iowa and someone informed him that Iowa is a farming state…they may or may not understand magnets but they’re probably really up to date on John Deere.

TLDR: he’s an important IGNORANT nut case talking to his poorly educated base and he’s trying to suck up.

To be clear, I don’t think farmers are poorly educated, but I do think his base (including farmers) is. He’s trying to speak their language.