You have to look for certain things then it's pretty clear. As Knight approaches him you can see his hands down low. As the bodies separate after the hit again you can see his hands and they are low. In the 30 frame per seconds world there's no way for his hands to come up and be back down. Also when you think about it the white jersey of Knight would be very obvious against a Duluth uniform or helmet.
And yes, I blame someone for repeating something that is obviously a lie when anyone can look at the video and see that it was NOT an elbow to the head.