Exactly what JCnGrace said. Keep it clean, but otherwise it should be fine. If you notice any more trouble, call the vet. If you want to help the swelling/heat go down, you can break out the hose and hose it down with some cold water, but it's probably fine without it.
It definitely could be worse! When I got my first horse I had her for about a week before she stepped on a short nail (it was a chance thing, the barn was very clean overall, we just got unlucky). I still have dreams about the blood gushing out of her hoof when they pulled it out. There were wraps, poultices, duct tape boots, stall rest... no fun!
Like your barn worker said, they bang themselves up all the time. Casper'll be back to normal in no time, I bet.