Draft horses like that (a Percheron, or maybe a Clydesdale?) are generally pretty amiable. This one did NOT like that balloon.
I don't think it was the balloon as much as it was the feeling of the ribbon getting wrapped around it's back leg.
When I worked fireworks at Disneyland the stables where all the animals that were in the park including the draft horses that pulled the street cars on Main Street were housed were adjacent to the fireworks launch area and the nightly shows didn't bother them a bit. They would walk the horses by the launch site on the way to their stables as were loading for the night's show.
When they broke ground for the new Star Wars land in 2015, the stables were in the cross sights for the new land so they moved the stables offsite to the city of Norco which is about 35 miles to the east and they now truck the horses into the park in the early morning hours and return them back to their stables in Norco around 3 in the afternoon when they need Main Street clear of the streetcars so they can run the daily parade.