Every time I watch this video, I keep thinking the same thing–he was “behind” the aircraft, distracted. He made an incorrect response to the ground controller. He was not on tower freq. when cleared for takeoff. He was still switching radio freqs and making radio calls JUST before rotation. SEEMS like he got complacent–way too casual with the radio calls, that’s for sure. Listen to his calls, again and again. You’ll see.