NFC with AES : how works the exchange of key
As in most Smart Card systems using symmetric cryptography, the reader does not hold a key shared with a card. It somewhat holds a master key which, combined with a card identifier (e.g. some serial number), can produce a so-called diversified key, which is in the card. This is known as key diversification (diversification is derivation using a master key and device ID). This insures that even extracting a key from a card can't compromise the key of other cards.

The reader-side cryptography is typically performed by a SAM, perhaps similar to this one.

Thus UID/RID might be the device ID used for diversification. Or not. It is not secret, most often can be read (at least in EV1) and thus cloned; but the associated diversified key can not be read, and that's what prevents cloning.