The original point was
explain how an object of that shape can travel so fast in the atmosphere.
and look, here comes the Ball-Brigade now claiming that it's common knowledge that objects can travel that fast in the atmosphere. I'm blown away...
Where you draw the atmosphere/space line is completely arbitrary. There will always be some matter, even in interstellar space, and it will slow you down somewhat. The point was, an object the shape of the ISS couldn't possibly be travelling at a lower altitude, in a denser layer of the atmosphere.
Further, the point is, the ISS is at a height you consider "impossible", and it's really there, you can see it yourself, anytime.