Calculate sum of absolute difference per pixel
I think there are multiple things to consider here:

1) Where are you dividing the image into 8x8 blocks? If you don't divide like this, then normalization by 64 is meaningless, and you are just computing SAD over all pixels. Maybe I'm seeing something wrong? You should do the normalized SAD in those small windows and then sum and normalize. And since 3600 is not a normalized value, I don't think that he normalizes.

2) Have you considered that your function for loading the video or the codec you use is actually giving you slightly different values than the one he uses? If your input is different, you will obviously get different results.