Horses and people with forms of Autism have A LOT in common. Based on my limited knowledge of horses, most everything that troubles Autistic people, also troubles horses. They are very sensitive to invasions of their space, and they hate being touched in many cases. Looking a horse in the eyes is very troubling to them, and can scare or anger them. Sudden noises, unidentified movements, or bright lights can panic a horse.
There may be a special understanding between horses and Autistic people, although I am not so experienced as to say there is a strong connection, beyond some limited personal experience.
Being very new to coming to a full understanding of my Asperger's, I have a lot to learn. I don't know exactly what a "meltdown" is, but speaking for myself, I would interpret it as that point at which it's just too much, and I need to cut everyone off NOW, and go disappear for a few minutes to a couple hours. Or is a meltdown that point where I have the instinct to clench every muscle, and shudder? I can control that pretty well, but I do feel it. If it's worse on most other people than it is on me, then it makes sense to call it a meltdown.
Charles