Re: Stupid Question
"If the keys were on a network not connected to the internet then how did they get them to their customers?"
Read up on Stuxnet.
Read up on the Equation Group (The Register hasn't covered this story much).
In plain terminology, usually enemy spies put stuff on internet-connected computers that gets hand-carried over to the victim's non-internet connected computers via disks or USB sticks.
There is also a history of some national intelligence agency intercepting US mail to alter conference proceedings CDs. So intercepting the physical transfer of information by mail or courier.
But they can also do spying via monitoring energy usage or physically copying the contents of the non-internet connected computers.
Nothing you can imagine as possible is impossible for the major state-sponsored spy agencies.
It does not matter how much care you take, the NSA, GCHQ, their Russian, Israeli, French and Chinese counterparts can get at your stuff if they decide you are a target.