The most likely scenario I see at this point is that the piece itself was mostly driven by WikiLeaks and Snowden gave approval to put his name to it. Perhaps he helped with some of the main points but it doesn't sound like him and it certainly didn't look like his writing. The 'political speechwriter' theory sounds the most reasonable to me at this point.

I'm not sure that going from "I love my country and want the people to know what the government is doing" to "FUCK THE US AND FUCK YOU OBAMA" (paraphrased!) is really the wisest course though. But what do I know?