Primary contact is irrelevant for targeting to be called. It's not in the rules.
For a defenseless player, which he was by definition, all that's needed is forcible, not primary, contact above the shoulders.
Was the contact to the head forcible? Thats a fair debate.
Bottom line to me is i dont think they wanted to disqualify a player from such a huge game. Or maybe they just didn't see the angle I've seen that seems to show forcible contact to the head.
This link provides a really good explanation, at least as the SEC calls it.
Targeting: College football's hard-to-define penalty.