The tops of trees or other fixed objects in the middle distance make it easier to gauge the effect of the wind on clouds or other high objects.
This aircraft is dealing with a serious crosswind, the effect is heightened because of the treetops.
Notice how the aircraft appears to be flying straighter at the very end of the video. It isn’t, we just don’t have the treetops as reference.
You might also enjoy:
The Heiligenschein or Halo Effect