The speed of light provides a limit on distance for a given RTT, and taking the examples in the article which are less than 0.5ms and considering the speed of light (300km/ms) the measured exit countries must be accurate.

The speed of light in fiber which probably covers most of the distance is also even slower due to refraction (about 2/3).

Thanks for your informative reply. I see now I was approaching this incorrectly. I was considering drawing conclusions from a high RTT rather than a RTT so small it would be impossible to have gone the distance.