All password managers allow copy-paste (which is what happened here) and the popular ones all offer you the ability to search and fill passwords from other domains. It's important to understand why they do, because it's also why these attacks continue to work: the user _thinks_ they are working around some kind of IT screwup, and 9 times out of 10 (probably closer to 99 out of 100) that's correct. Every marketing-driven hostname migration, every SSO failure, every front-end developer who breaks autofill, every “security expert” who was an accountant last year saying password managers are a vulnerability helps train users to think that it's not suspicious when you have to search for a different variation of the hostname or copy-paste a password.

That's why WebAuthn doesn't allow that as a core protocol feature, preventing both this attack and shifting the cost of unnecessary origin changes back to the company hosting the site. Attacking this guy for making a mistake in a moment of distraction is like prosecuting a soldier who was looking the other way when someone snuck past: wise leaders know that human error happens and structure the system to be robust against a single mistake.