Sorry; 'tain't true. That's one of many myths about the shooting sports.
Everyone looks thru sights/scopes differently.
The sight picture doesn't change but the person shooting the gun does.
Two people shooting the same gun can get two sets of consistent results because they may:
- hold the gun differently
- perceive recoil differently
- and yes, even see the target differently through a scope because of the way they are holding/resting it.
I have experienced this with handguns and long-guns between family members. One person's zero with a scope may not be another's. There's usually a one or two click adjustment. This is doubly true with handguns/iron sights and those who are cross-eye dominant.
Maybe this is a better way of saying it...
It's not the sights but the way the firearm is held that requires a different zero with the same firearm.