>He didn’t remember his password, and we were unable to reset it because you need the passkey! No other options to authenticate for a reset were available.

Google treats both a password and a passkey as a primary factor, and if you forget either of them you have to go through their account recovery flow: https://support.google.com/accounts/answer/7682439?hl=en

AFAIK there's nothing different about the recovery scenario for a Google account in that state regardless of whether it has a password in use as its primary cred, a passkey in use as primary credential, or both.