You're assuming a single piece of information has a single key-pair. E.g.:

  1. Obtain sensitive information
  2. Generate a new key-pair
  3. Encrypt with public key
  4. Store encrypted info
  5. Delete public key
  6. Use private key to decrypt when reading the data

It's also likely they they were using one key-pair to encrypt all of their data (or all of a specific type, e.g. one key-pair to encrypt all passwords). In this case, the public key would be needed to encrypt new data coming in.