If you ordered a PureBoot Bundle or anti-interdiction order, then the public key on the Librem Vault corresponds to the set of private keys we generated on the Librem Key at the factory. It’s intended to give you a backup in case you wipe out the keyring in PureBoot and want to re-add the factory-generated key. In our PureBoot Getting Started Guide we recommend just using the factory-generated key to verify your firmware wasn’t tampered with during shipping and then replacing it with your own keys, possibly using the OEM Factory Reset feature of PureBoot. That way there’s no chance that someone at Purism could have a copy of your key.
While you could share that public key with others and use it for encryption/decryption/signing (as it’s just a standard GPG key), I’d recommend generating a different set up GPG keys for that purpose so only you could have had access to them (and also so you can create a backup–the keys that were generated on the Librem Key can not be backed up or copied off of the device). If you want to generate new GPG keys you can follow our Librem Key Guide.