I believe the cause is mainly the camera's "corrective" processing ability.
Here in this thread on reddit, "antiqua_lumina" made a video of some balloons, floating steadily, while moving the camera..
Hey everyone - since there are a lot of amateur videos around this sub, I had a good opportunity to make a demo when I noticed a set of balloons flying by. You can see when I move the camera around that the balloons appear to move erratically too. I can assure you they were slowly drifting up and not to the sides and did not suddenly accelerate.
Equipment: iPhone 12. Default camera app. 4K at 60fps.
Just sharing this as a demo to help hone the community's discernment when analyzing footage.
Most of the effect here is parallax against the nearby leaves as the camers is moved around, with the movement of the picture being "stabilized". There's still some parallax against the roof edge, but not as much. I'd love to see a version of this clip stabilized on the balloon.