If the user is logged in under a different name, then they registered for the meeting with, when they join the meeting, their logged in Zoom name will override the registered name. The user_id field will also be overridden by the id of the logged in user.
See my post here for more info:
That being said, I wouldn’t create a Zoom account for user B. They can simply join the meeting without an account using the url returned from their registration. Then all the values should line up.