It throed out many possibilities. Like slowly sinking. We found out that the Eng. had guessed correctly.

The simple answer to your question is, it doesn't.
There are literally hundreds of thousands of bits
of debris floating around in orbit. NASA actually
tracks thousands of them, ones big enough to
cause serious damage. But there is no way to
track all the bits. Most are too small.
I recall reading an estimate of a 50% chance of
the ISS being hit by something large enough to
destroy it within the next 10 years. So, given enough time, it WILL get hit.
What they are counting on is being able to catch any particularly dangerous pieces coming towards them which are already being tracked. But for right now, they are sitting ducks.