It is understood that a desk officer kept him talking while an armed unit was scrambled to the scene, and he was arrested.
Speaking to reporters, Sir Peter said: "We are not confident that we have recovered all the grenades, we don't know for certain, so we've made it clear to our officers that the threat is still there.
"I would want that to be the message, this has been a long-standing criminal feud between different outfits in Manchester and in the Tameside area, and that threat is very much there."
He said that the force had issued Osman warnings - notices given to people under threat of being murdered or seriously injured - to "a large number of individuals".
Sir Peter had suggested that the two officers were lured to their deaths, telling a press conference that a call had been made reporting a burglary at the address. The force added that one of the officers' Tasers was found on the ground out of its holster at the scene.