Similar triangles would say that to be 2" off at 25yds your eye would only have to be ~.06" off - assuming the distance from your eye to the gun is 2'. It wouldn't account for big changes, but it could account for something. I don't think it's that unheard of for two people who shoot well to shoot the same gun to a slightly different poi.
Bob seems to know what he's talking about, and I'm willing to believe that he's not lying about his poa changing after his surgery, so something must have happened. The eye's point of focus shifting was my best guess. I could absolutely be wrong.
si vis pacem para bellum