This is what happened to my dog (Std poodle, truly harmless and I say this as an experienced dog owner). I take her to walk to a park where dogs can be off-leash certain times of day. That day, we met another off-leash dog who seemed friendly too. They sniffed amicably, until the other dog attacked mine, and viciously. And yes, it was a pit-bull or pit mix. I looked at the owner - the guy was dumbstruck, literally, so I jumped in the fray, literally rolling on the ground trying to pry that dog from my dog’s front leg. And I won’t lie - right then, I was going to HURT that dog. I hit and kicked and she finally let go. And the owner says “She’s never done that before!” My dog limped for a couple days but was fine, fortunately.
She was also attacked by a huge dog who was on the leash! and whose owner let him go too close to mine, until he jumped on her. Some owners have NO CLUE of their dog’s warning signs.
As for the horse being attacked video - not watching that. But as a rider, in this situation, you bet I would have been on the ground kicking and yelling at that dog, in a heartbeat.