The roll rate appeared to be proportional to the visible control surface deflection. In other words, the roll appeared to be commanded, rather than inflicted upon the aircraft from say rotor, as has been suggested, which would be countered by the opposite movement of the control surface from that seen. It would be interesting to learn whether it was intentionally or unintentionally commanded.
Either case would require some explaining, now that this is published for everyone to see, with both inside and outside views confirming the roll commands and the associated quite obvious effects on the aircraft. It seems highly unlikely that it would be commanded by the autopilot.