Also what exactly made you think he was exaggerating?
I have the same feeling. I have not read his book but watched his interview with Joe Rogan and honestly he sounds borderline delusional. Just jump to 1:05:20. I just find it hard to believe that a low-level contractor can do this.
"so now I come in and now I'm the sole employee of the office of information sharing but I'm not close enough to retirement that I'm ok with just doing nothing at all so I get in business and I come up with this idea for a new system called the heartbeat and what the heartbeat is gonna do is connect to basically every information repository in the intelligence community both at the NSA and across Network boundaries which you normally can't cross but because I've worked at both the CIA and the NSA I knew the network well enough both sides of it sides that normal workers at the NSA would never have seen because you have to be in one or the other I could actually connect these together I could build bridges across this kind of network space and then draw all of these or records into a new kind of system that was supposed to look at your digital ID"
This quote that you posted got my attention as well when I was listening to the rogan podcast. He's basically described building an inter-org (cia-nsa) middleware as a storage admin. Snowden isn't a developer / programmer, so I'd love to understand how he built his so called "heart beat".