Dual Window display during meetings

I have a client that whenever he gets invited to a Zoom meeting via Outlook email, he gets a dual window display. I checked his settings > general tab > and the Use Dual monitors is already unchecked. 

He says that when he joins the meetings, two names will display, his name and his name and last name. That's what creates the dual windows.

Does this have anything to do with the meeting invite? or is there a setting in Zoom that I missed?