He hasn't taken a deep-dive into the protocol, as you can see from his quote regarding 51% attacks - he views that as a fatal flaw, as the rest of us understand that such an attack takes enormous resources not only to mount, but to maintain such a position.
Not to mention it would be kinda pointless for them to do as far as I understand.
I think he has other things on his mind, most notably extending his stay in the former USSR or getting asylum in another country to prevent his extradition. That's what I chalk it all down to, he read some bullet list somewhere and didn't really take the time to consider the system in its entirety.
Another credible interpretation is that he is a propagandist, using his "credentials" to promote the views of his handlers. Snowden is a very suspicious character when you look closely at the details surrounding the events of his 2013 "manhunt" and of his life history in general.
What was suspicious about him?