Until I learn more I'm going to take the 50TB accusation like the (as much as) 300 years jail time they're likely threatening him with to get the plea deal. Sound like there might be some funny counting going on.
My guess is he was addicted to "stealing", the same way some people shoplift for the thrill. It can feel empowering to steal because it gives the thief control. So subconsciously he's thinking "huh, NSA thinks they're so tough and powerful, but look how I can break their rules right under their nose and they can't even figure it out". Or perhaps he exfiltrated people's phone calls/emails. Thats another power theory: "I'm as big and mighty as the NSA because I can tap communication lines and invade privacy just like they can".
Like others in this thread, I dont think he was a spy. A spy wouldn't hoard shit in his basement that could get him life in prison. He would have stolen it, sold it, and GTFO.
$ echo 20*10 | bc
200