Absolutely wrong.
When your eyes focus on something on the distance, you lose focus on things not in your central 20 degree vision cone. But things do not become bigger and your FOV does not decrease. You still see everything around you, except that the focus is on something farther away. And Depth blur, which this game has, can simulate that perfectly. All they need to do, is to add a progressive blur to distant objects which is pierced through when aiming down the sights.
ACOG zoom is not the solution.
This is an example from Stalker, a game from 2007. It uses depth blur to make distant object unfocused and the same technology is used in RO2, however only for the blurring of foreground objects when aiming down the sights. If they would apply this on the distant objects too unless aiming down the sights, then the problem would be solved.