Isn't the reason for the popping the fact that the dirty air goes back into the motor. And how would unplugging the hose from t
he air box and putting a filter on it change how much air vents out anyway?
There are at least three things needed for something to "burn". Oxygen, fuel, high temperature...the higher the better.
On deceleration, filtered air is being allowed to go from the airbox, through the vacuum-operated valve, and into the exhaust. This filtered air contains about 20.9% oxygen (compared to almost no oxygen in the exhaust that just exited the cylinder into the pipe), and the incompletely burned fuel that just exited the cylinder is THEN burned in the pipe (Oxygen, fuel, temperature)....POP.
Some people call it "lean pop", which isn't telling the entire story. Lean burning exhaust is hotter than rich burning exhaust...so, the exhaust pipe is hotter. It is hot enough to stimulate whatever unburned fuel there may be, to then ignite in the pipe....POP. This time, it's because the temperature is so high (remember, the higher the temp, the more likely to ignite) rather than due to the introduction of oxygen (as in the PAIR system).
At least, that's how I think about it. Maybe it's not entirely correct...I'd be interested in a more correct explanation if someone has one.