The article says you can recognize a human as a human at a little over 2 miles. However with cheap binoculars at a much greater distance. Taking a wild guess binoculars with a magnification of factor 7 would push the 2 mile limit out to 14 miles given a crystal clear atmosphere (and ignoring the curvature of the Earth).
Binoculars!
Earth’s curvature does not matter at Trumps elevation relative to distance to WTC.