The question is if it was forcible contact, which again isn't defined by the NCAA. I don't think anybody can say it was clearly forcible contact when that isn't even defined and there is a question where the contact was first made by the defender on the WR.
Again, I think this could have easily been flagged - and hits like that often do get flagged. But also think there is some justification for the no call given the technical requirements of the rule as defined by the NCAA.
I also think it's silly to claim that Big 10 refs willingly cheated to help the SEC, which many seem to want to think. I'd bet it's as simple as the crew determining that there was no video evidence of forcible contact and so they declined to make a game changing call without it.