You used a third party app, not Apple Wallet. Hence what I wrote above would not apply to you. Third party apps are not stored securely in the Secure Element or Secure Enclave.
Evidently you didn’t complete a final step or two when erasing the device. You needed to turn off FindMy if enabled for the device and remove device from your Apple Account.
Pass2U may have iCloud storage and syncing privileges if you enabled it in your iCloud Settings on your iPhone.
Please follow this path,
iPhone > Settings > Apple Account (Your Name at top of screen) > Save to iCloud – See All > scroll down > Pass2U > disable.
iPhone > Settings > Apple Account (Your Name at top of screen) > Drive > Apps Syncing to iCloud Drive > scroll down > Pass2U > disable