Actually, I have heard this from several levels, book study conductor, elder body, CO and DO.
The idea is that people shut down at the door as soon as the hear "jehovah's witness."
They thought somehow they would fool people into thinking that jws were not at their door. Like who else would it be, eh?
I've pointed out that the "suggested" presentations in the KM conveniently leave out saying "Jehovah" and there is no suggestion to say "we're jehovah's witness" in the beginning.
This is a case of speaking out of both sides of their mouth
1) Saying that a witness is given when people look out their windows and see jws
2) Saying that non-jws don't know it's jws they see outside their windows coming to their door