You can shoot with high depth of field and not cause motion sickness. Aerial videography does that every day, and it's no more difficult in general to parse than looking out an airliner window or at a distant horizon would be.

I suspect GP is closer to on the money here, in suspecting the issue lies with a semblance of movement that isn't like what we see when we look at something a long way away.

I didn't notice such an effect myself, but I also haven't yet inspected the videos in much detail, so I doubt I'd have noticed it in any case.