I have heard some Priests say that they are unable to remember anything revealed to them in the Confessional, but as far as I know most do not have this gift. It is certainly not a teaching of the Church that Priests don’t remember what you say in the Confessional.
It is, however, Church teaching that a Priest may never reveal what he learns in the Confessional, even to the person who confessed it [unless that person brings it up first and/or gives him permission].
As a practical matter, however, I think most Priests would be hard-pressed to distinctly remember a particular individuals’ confession…simply because he hears so many of them. Usually at my Parish we have ten or twenty people confessing at each scheduled time (sometimes more, sometimes less) between two Priests. I would guess that only particularly distinct or unique confessions would ‘stick’ in their memories when they hear 20 or more confessions each and every week!
That might be different at a smaller Parish, of course.