So my s/o is a horse person. I showed her this video, and she says the horse is displaying excitement, not aggression... like when you return to your dog after an extended absence, or open up the treat drawer.
When I was a little kid I used to go see my Grandma's old school friend Peter and he was a camera man & film set builder for David Attenborough with his farm being filled with all sorts of crumble churches, rabbit warrens, detailed sewer systems etc. The best thing about visiting wasn't any of that stuff, but his awesome miniscule horse named Brandy who lived in and around his enormous house and ate almost anything a kid could dream of feeding a tiny horse. He was cool.