I'm 46, been messing around with computers since I was 22, yet for some reason I'm having a really hard time understanding this system. My actual job is helping people understand technical systems and selling them on the benefits, yet here I am feeling clueless. As soon as I think I understand something it seems that's wrong, or even dangerous.
The key is in understanding some cryptography concepts, in this case primarily Public-Private key cryptography.
You also need to understand the 'compromised keys' comments in context. The context can be found in the minds of cryptographers. Paranoia rules (with good reason). The rules are black and white. Something is only secure if it can be mathematically proven, so even the perception, however slight, and in real life, however unlikely it is, that a secret is compromised, it will be labeled as such. It makes it easier to talk about these concepts as there is a clear boundary between what is secure and what not and what lies inside this boundAry.
So labelling something as 'compromised' means that it is not protected by a cryptographic boundary anymore and is now probably only as secure as the rest of the files on your computer. By no means is it exposed to the whole world all of a sudden.