It's that whole "you can't hear a person's tone or inflection in an internet post" thing.
Plus, some of us are familiar with MM's posting style.
If you've ever worked around cattle, you'd be inclined to discount the whole "run into the fence" thing. That calf might have behaved in exactly the same way without the horse close on this heels, the holding pen with his buddies was at the same end of the arena. Newly penned cattle will run into and run up the fence like that without any extra pressure. The horse and rider were that close because, well, it's a whole lot easier to rope from close in.
That said, I'm not always wild with the way rodeo stock is treated, particularly the way calves are thrown and tied. At the end of the local rodeos, the calves get smart, and by the end of the day they practically lay down and hold three legs up when they feel the rope. A cowboy acquaintence of mine refers to it as "the cattle are soft"
Sarhvr, Don't feel bad. They make videos like that because playing on people's emotions in that way is effective. They wouldn't do it if it didn't work.