This is obviously a test, and safe to say the vehicle was out of control and not entirely predictable. I realize they wouldn't fly into the actual predicted landing area, but just being close must be a risk.
Would the flight crew on that plane literally be scanning the sky above them to make sure they're not in the direct path of whatever comes down at whatever speed?
Let say they are cubes of 30m each. The expected area where they might both be present to be a 5km square. That's a 0.000025 chance of collision at most; and I suppose the plane is away from the center of the expected Starship Gaussian. I'd personally ride in that plane and risk that, even to just to get a glimpse of the reentry.
Somehow I was thinking it was super risky to be in the general area, but your numbers show that is clearly no the case.
Once Ship finished burn it simply had to land in predicted landing area in Indian Ocean, it did not have enough fuel on board to significantly change trajectory even if computer went crazy.