Responses
It’s a myth to be exact. Cows are actually colourblind. They only get excited seeing the flapping of clothe, regardless of colour. You see in the chapter, they started charging aggressively after mother-in-law’s coat flapped
Yes it is a myth, but it's a recurring situation in fiction, that's what makes it a trope. Tropes aren't always false, but they aren't always real either- any situation media shows over and over again in fiction is a trope regardless of reality.
The cow fight is because it's an old trope in Western fiction (Europe, N America, etc) that "the color red makes cows aggressive" supposedly. Her red jacket supposedly put the cows into a frenzy.