A relation (taʿalluq) specifies how knowledge is connected with its object. Speaking of this relation is distinct from speaking of an alteration in the underlying attribute.
Zayd's location at one time differs from his location at another. But that difference does not prove that God first lacked knowledge and then acquired it.
The reply does not claim that eternal knowledge functions like human memory. It simply denies the inference from changing external states to intrinsic change in God.