User associated with wrong account

[bear]

Had an existing client create a new account for a new project, but intended to have it separated from his existing one (login, manage, all of it). He used a new email, but the same name (his), and it somehow created the new account with the new email, but added his user with the new email as a user on the OLD account. He's very confused, and so am I. This new user system is not at all simple to manage, and unless it was his error in the first place, it seems like WHMCS added him because of a simple name match.

If I delete that user from the old account, the docs seem to indicate that will remove him entirely, including his legitimate 2nd account that uses that new email. 
Do I have that right?

How does one remove that user from the old account then? Is it as simple as changing the email in the user profile on the old account where it doesn't belong to the old one ( making owner and user  have the same email)?