They didn't arrest him, so no.
This is harassment of political dissent by the policing arm of the government. What makes this even worse is that it's the British government harassing a Brazilian national for the sake of American intelligence.
This is how they see him. They see this in an extremely black and white way. Secret documents were stolen. Miranda is handling stolen goods. The Guardian is aiding and abetting terrorism. QED, we can use the terrorism act to stop and search Miranda.
I kid you not, this is their psyche. This is how they perceive these leaks.
Of course they do. That's why they're harassing people that dissent from their black and white views.