When i zoom in on zombies at a distance, medium and even long distance they are alerted to my position and come running.
I have recreated this many times, 6/10 times, mostly in towns, city's and docks/harbor areas.
i have tried it in urban / country side areas and fields a bit and not noticed it there yet.
i have even managed to lure a zombie from very far away, one time only, it was far away that you couldn't see it with out zooming in.
Don't know if bug works on short or very close range.
it can lure / alert more than one zombie at the same time, it worked for 3 zombies one time that were near each other.
seams like a high chance for bug to work if you move around side to side.
Bug has worked while standing and crouching (did not try while prone)
I haven't tried it or made it work on any zombies facing away from me, maybe bug works for zombie facing away.