It doesn't seem particularly likely to be incorrect. That area of north-east Germany was kind of a backwater in late antiquity, with the Romans stopped well short of penetrating that far, and many of the tribes that had been living there migrating further west, and replaced with the Wends, a branch of pagan Slavs.

800 CE would be about the time that that area of Germany became part of Charlemagne's empire, and Christian missionaries started making inroads around the Baltic.