The mustang skull itself will need to be carbon dated before it's purported age can be considered legitimate. Until then, it must be considered of dubious merit.
That being said, when it finally is carbon dated, if it does turn out to be legitimately pre-columbian, then it is probably one of the most significant finds in archeology.
I'm not cherry picking the report, you are. As the anecdotal evidence points to an entirely different mound for the later introduction, there's no chance for the anecdote to have any bearing on it. No one in the report is accepting anything "based on faith", but the attitude that the horse was extinct in the Americas until the Coronado expedition reintroduced it -- an event for which there is testimony in firsthand accounts of the expedition, I'm sure -- is nothing but faith. Whether the horse was reintroduced is the question.