Come on WojtekSz, achieving the best gliding distance is done by flying at best glide speed in the cleanest configuration (no flaps or ld gear) and certainly not by pulling on the nose till the minimum speed. When you have headwind you even need to increase speed over best glide speed. I don't know the best glide speed of the 777 in flaps 25, but it's usually very close to Vref.on many aircraft. The more you deviate from that speed, the more you shorten your gliding distance.
There are certainly many explanations for the late AP disconnection, but you can't seriously pretend it was intentional in order to extend the gliding distance as it's clearly achieving the opposite. Retracting flaps was not all as some people seems to believe, speed control is much more important in such situations.