These are two project team member records, and they point to the same bookable resource records, then relate to user.
When you create new project team member, you can select any bookable resource, though it is selected in other project team members.
It is by-design.
If you don't want to show resources that has related to other project team members when you create new, maybe you can try to filter 'Bookable resource' lookup view as following screenshots.
--Make the lookup view show only resources that are not related to any project team member.