NFC can transmit arbitrary data, too (which is done on bt pairing, as the two devices exchage a bluetooth passkey). As the data rate is (relatively) slow, there is no sense in transmittig big amounts of data (like directly sharing an image via nfc). but as a keyboard has to send a minimal amount of data, nfc is fast enough. there is no standard for this though, there will be a special driver needed, which is polling nfc and emulates the keypresses for the os.