Are you sure you don’t know them or that they aren’t a friend of a friend? 🙂
If not, it likely means free agents or another small group has been merged onto your team. When groups do not reach full team size we merge groups and free agents together to fill out rosters.
To learn more about our how the roster management and group / free agent mergers work check out our full roster management page.← Why are there people I don’t know on my roster?