(I should have read ahead, just realized this has been explained several times already.)
What Fatrick is referring to here is Kessler Syndrome. Essentially, every time something is damaged in space, it produces debris. The more debris there are, the more likely collisions become. This increases exponentially, extremely energetic particles large and small slamming into each other at breakneck pace, eventually enclosing the earth in a cloud of violent shrapnel that is fed by any attempt to launch anything. Ripping apart whatever we try to put up there.
https://en.wikipedia.org/wiki/Kessler_syndrome
It's a genuine issue that is becoming increasingly possible as we accumulate objects in space. Keep in mind space is already full of tiny particles that bombard our machines there. His skulls just so full of cholesterol that he's bad at explaining it.
Essentially, if you've got 2 sattelites you can cause a large problem by intentionally causing a collision in a stable, well trafficked orbit. If you have thousands of satellites, you can kick start Kessler Syndrome all on your own.
That being said, any private individual who did this would be on the receiving end of the ire of every state on earth and it'd probably require someone genuinely psychotic with a large number of collaborators to pull off. That musk might do it (except by total accident, poor communication, or an actor sabotaging him,) is very unlikely.