Horses have very acute senses because they are prey animals, and they simply would not have survived in the wild if they were not acutely aware of their surroundings. However, the majority of their instincts are "self preservation" rather than "help my rider or herd mate." A mare will have maternal instincts to protect her young foal, and a stallion may try to protect his herd from other interlopers or predators.
Horse herd instincts tend to be more related to safety in numbers, where the weakest will not survive or outrun the predator. Their first instinct is usually flight (run away), but if they feel cornered, they will fight. So it sounds as if the movie was portraying the horse in the "Lassie" role, which is unrealistic relative to normal equine behavior. That does not, however, preclude you from enjoying the movie!
