Note that that's in the sense of angular separation, as viewed from the ground. They're physically hundreds of kilometers apart.
edit: (Geostationary orbits are ~42,000 km from the Earth center-of-mass; each degree of angle is an arc of ~700 km).
That’s pretty close when your neighbor just exploded and there’s almost exactly zero air resistance to prevent debris from reaching you.
If you have a 25 m^2 cross section in the direction of the explosion, at that distance you have a roughly 1 in 246 billion chance of any given bit of debris hitting you.
When calculating risk, you have to take into account how many are there and what is the chance that any will be hit. Then you have to calculate what's the chance this will happen again, etc - and only then you can calculate the risk to your own satellite.
It's true that the chance of getting hit by one broken satellite is small. But that assumes there are exactly 2 things on the orbit.
[0] https://en.m.wikipedia.org/wiki/Kessler_syndrome [1] https://en.m.wikipedia.org/wiki/Neutron_flux