The Person List shows you every non-public person who is in your family group tree. Remember that it is a family GROUP tree, and so anyone in the group can add living profiles to the FGT.

You can go to the profiles for persons you don't recognize, and look at the list of recent changes to see who added them to your FGT. You can then contact that contributor to ask who they are and how they fit in the family. In some cases you may need to add additional living profiles or at least add relationships to deceased persons in the public part of the tree.