animal communicators, horse whisperers, whatever you want to call them, if they're any good at all, have to be really familiar with horses and people both, so they can get cues just from observing you. You might not be aware of how much a really perceptive person can pick up just by noticing details about you, how you dress, where you are, how you present yourself.
AND as someone else pointed out, a lot of what is true about your horse is true for any horse or most horses.
I think they are primarily animal behaviorists with excellent observational and marketing skills, myself. Read Sherlock Holmes sometime for an education in how telling the tiniest, most insignificant detail can be.
don't worry, spiders, I keep house casually.
~ Kobayashi Issa
(1763 - 1827)