We used to family camp at a trail ride near the north rim of the Grand Canyon.
The horses knew they had tourists riding and they knew every trick. They would scrape riders off on trees and they vastly preferred going downhill or back to the corral.

One time a rider didn't come back. They found him still on the back of the horse about half way around the trail in the middle of a meadow. He couldn't get the horse to move and he was afraid to get off because he didn't think he'd be able to get back on. Ha, ha.
The horse decided to end the day and spend time in the meadow eating grass.

Horses definitely aren't dumb (with a few exceptions of course. Like people.)