Peter,
Guests can upload their Gedcom before they volunteer and become full members, and by doing that can see if they have possible unfound ancestors, or family members already here :)
To populate their branches by that Gedcom, they would need to become a full member. Sometimes they do not choose to become full members and therefore their Gedcom would either be deleted by them or by default at a later date. However, the badge is automatically awarded when the Gedcom is first uploaded, so will show on the profile regardless :)