It did...and so did Sham who most likely would have won the '73 triple crown had it not been for Secretariat. IIRC, the original use of the term, "X factor" was for the oversize heart of a racehorse, and is believed to be a recessive trait in thoroughbreds that can lead to a healthy heart being 2X (or even more) larger than a "normal" horse heart.
Thanks!