I'm guessing the person on the phone when hearing suppressor was thinking flash suppressor/muzzle break and not silencer. I can see in this case where washers/shims might be used in order to index the muzzle device properly. Yes no maybe? I know squat all about silencer construction and what-not but I have seen other muzzle devices that need to be oriented specifically and would imagine this is accomplished via the washer/shims mentioned.
Or I could be so full of **** I stink, as grandma was fond of saying occasionally.