The arrest of the insurgents and the lack of attacks in the area may or may not be related.
If there were no attacks actually planned, the arrests accomplished nothing.
And that's the problem. Prisoners subjected to abuse will tell the interrogators what they believe the interrogator wishes to hear, not necessarily the facts.
Now, if you're one of Saddam's boys, you don't care about that. But we're not Saddam Hussein's Mukhbarat.
An untrained interrogator will tell a prisoner far more than he or she intends to--and, if dealing with a real, genuine insurgent, far more than the insurgent will ever tell the interrogator. One thing that will ineviatbly happen is that the amateur will ask leading questions that tell the prisoner what the interrogator's biases are, and what the desired answer is.