It usually happens for one of two reasons:
Digital Wallets (Apple/Google Pay): These services use alternative numbers for your card number for security. The last 4 digits on your loyalty account will match your Apple Pay/Google Pay number (it may also be listed as a Device Account Number, or Virtual Account Number), not your physical card.
Mistyped Number: Another guest may have accidentally entered your phone number during their checkout. You can safely delete any card you don't recognize. Please note that once deleted, a card cannot be re-added.