... I specifically denied the fact that the aircraft was even climbing..
Watch the video. The part around the Clifton Bridge starts at 1:43. The plane flies almost parallel to the ground and rather low over a flat terrain. Then, at 1:59, it starts to climb in order to keep the distance over the approaching hills that carry the Clifton Bridge. Yes, it makes the turn at the same time, which exaggerates the appearance of the angle of climbing. However, it started to climb before making the turn.
Back to my initial claim, that the plane was flying at relatively slow speed. Watch the video from 1:43 again. As it approaches the helicopter, the plane clearly appears to be moving faster than the ground underneath. However, at 1:59, as it starts to climb, and simultaneously flies by the helicopter, the ground appears to move faster than the plane, and the plane appears almost stationary for a brief moment, relative to the helicopter.
At that is the gist of my argument: slow relative speed. It matters much less if it was climbing, turning, landing, approaching, etc. What matters is that it was flying at a relatively slow speed (especially relative to the helicopter). It was slowing down, in preparations for landing. It takes a lot of slowing down from its max speed of 1,354 m/h (even if it wasn't used during the last flight) to the landing speed of 184 m/h.
https://www.youtube.com/watch?v=yr0v64evBxc