They were brute-forcing a PGP-encrypted ZIP archive, which would have been symmetric encryption. These kinds of archives were produced by the PGP Desktop appli

They were brute-forcing a PGP-encrypted ZIP archive, which would have been symmetric encryption. These kinds of archives were produced by the PGP Desktop application (at least in earlier versions; I don't know if it still does) and were functionally similar to using "gpg -c", although the actual file format is/was different and incompatible. Had the guy used a public/private keypair for encryption rather than a password, I suspect the work needed to bruteforce it would be much greater. But that doesn't look like the situation.