His lack of technical expertise is a very good reason to doubt his conclusions.
We've consulted on a few local cases of suspected computer sabotage. (Hurray for small-town politics.) In only one did we find actual evidence of wrong-doing; in every single other one, the case was an otherwise reasonable person whose suspicions were being fueled by a knowledge of I.T. based only on what they've seen on TV, in the movies, or read in magazines.
What Snowden did was remarkable specifically because it involved a huge pile of evidence. Conspiracy theorists are quick to point to this and say, "see, see, we've been right all along, and we're still right", but they don't understand that being right without any evidence is useless.
So articles like this one pollute the discussion that we all get to have thanks to Snowden's and Greenwald's efforts. Articles like this one erode their achievements.
This journalist doesn't seem to have consulted even one technical expert; he doesn't seem to have inspected the safe to gather any evidence whatsoever that it was tampered with; he doesn't seem to have taken a picture of a supposed spy who was assigned to take him around a city. In short, this journalist is not in any way contributing to the discussion that we get to have over the state's surveillance capabilities.
He's written a book about Snowden. He should know better.