The "guide" is 100% responsible. He let a client turn loose an unproven dog that went straight to the mules and then it latched on to your boy's neck!!! That dog would have never left the woods.
X100
I hope for a speady recovery for your son and this doesnt brake his spirit, but sounds like he is still high spirited, but a concusion could have happened with the sudden stopage of his brain inside the skull. he might want to get an MRI just to be on the safe side.