PM Burnham says the UK Government "can confirm our belief that we believe Iran to have played a part" in the RAF Fairford incident.
I can confirm Iran's belief that releasing supposed terrorists working for foreign states really says it all.
You're barking up the wrong tree.
They wouldn't have released the suspects if they thought they were doing any kind of armed attack. Considering the way the regime has thrown the book at peaceful anti-genocide protesters, I also doubt that they would have released them if they thought they were political activists.
In mind the two most likely explanations are that this is either some kind of dumb misunderstanding or that it was a false flag operation.