The horse you mentioned here just seems quite playful,I used to own horses a while ago and they do develop their own personalities. There are a ton of measures you can take to keep a horse from being bored as well,you can get these large balls for the horses to knock around and kick at and it keeps them entertained. There are a ton of other things you can do with them as well so that they do not get bored,even having another horse can help with that,but you still need to go out and pay attention to them. Brushing the horse and talking to them each and every day will help with the boredom as well,and it can be soothing for both you and the giant loveable animal. Horses can be fun and even funnier when they pull pranks like this one did,their good for a great laugh.