Actually, the fact that young Spock was an outcast was already established by the early '70's thanks to the animated series’ episode “Yesteryear”, written by D. C. Fontana. For the most part, this was only episode of that series that was considered canon until ST: Enterprise incorporated more of that series into official lore.
It was actually established in 1967 in "Journey to Babel", when his mother said "When you were five years old and came home stiff-lipped, anguished, because the other boys tormented you saying that you weren't really Vulcan. I watched you, knowing that inside that the human part of you was crying and I cried, too."
